Introductory Exercises for GIS Using ArcMap & ArcCatalog

Introductory Exercises for GIS Using ArcMap & ArcCatalog GIS Cyberinfrastructure Module EEB 5894, section 10 Please refer to the ESRI online GIS Dictionary for additional details on any of the terms in bold: http://resources.arcgis.com/glossary

Part I: Acquiring Data, Setting up Data within ArcCatalog & ArcMap Important Topics Covered • • • • • • • • • •

Downloading Data Using ArcCatalog Defining Spatial Reference Properties Creating an ArcMap Project Adding Data Layers Renaming Data Layers and Data Frames Zooming and Panning Creating New Shapefiles from Selected Features Extracting Data Creating Data

Downloading Geographic Data Real world features are made more manageable by generalization or abstraction of data. They could not possibly be represented precisely because the amount of data storage would be too great. These real-world features are represented as spatial data by points, lines, and polygons, plus grid cells or pixels. In GIS there are two types of data models used to convert geographical features into digital representations. The raster model divides an area into a grid comprised of a series of “grid cells” or “pixels” where each has a value assigned to it. This grid can be of varying resolutions where the smaller the cells the higher the resolution. A vector layer uses an (x,y) coordinate system to represent geographic features. Features can be represented as points (a single coordinate), lines (a string of coordinates), and polygons (a string of coordinates having closure). These features are also given a topology defining the neighborhood relationships among the features. The Map and Geographic Information Center (MAGIC) at the University of Connecticut has extensive data sets available online that anyone with access to the Internet can download. Some of these layers will be used to create a project in ArcMap. First spend some time browsing the different types of free GIS data that are available.
Using a web browser, go to the MAGIC website by typing in this URL: http://magic.lib.uconn.edu/ Your screen should look like the one shown below:

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Under “GIS Data” select “Hydrography”

This will show all of the state-wide options for hydrography data. For this project, we want the seventh entry in the list, “Hydrography- Line Features” from CT DEP in 1984. Data can be projected in many ways in GIS. One common way is to display all features on a flat surface with distorted distances (from “spreading out” a round object on a flat surface), using latitude and longitude only to specify point locations. This is called a geographic coordinate system and MAGIC provides data in WGS 84, which is a widely used geographic coordinate system. For small geographic areas distances may not be very distorted, but this can become an issue at larger scales. Another way of displaying data is to preserve distances or areas, thereby making the 2-dimensional display of the data appear somewhat warped or distorted (but suitable for measurements). These are called projected coordinate systems, and MAGIC provides data in the Connecticut State Plane projection. A shapefile is a common method for storing vector data and is comprised of multiple inter-related files. Another (older) method of storing vector data is coverages; these are also comprised of multiple inter-related files. Here, we will be using projected coordinate systems (CT State Plane).


Before downloading data, create a new folder somewhere on your computer to store all of your GIS files, such as C:\GIS_exercises.

Please note that for the most used types of GIS data, file paths with spaces work fine. However, some data types (including one we will be using here) require that file paths contain no spaces. Please create your new folder in a location without spaces (for example, don’t put it in “My Documents”).
Click on the appropriate CT icon to save the Hydrography layer, which will be downloaded as a zipped file named CT_Hydrography_1984.s24.ctdep.line.zip.

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Now scroll to the section labeled “Roads & Transportation” on the webpage and select the projected shapefile for “Connecticut Roads-1984” from CT DEP in 1984 (9th entry in this section). Download the zipped file named CT_Roads.1984.s24.ctdep.zip to your newly created GIS folder. Scroll up on the webpage to the section labeled “Boundaries” and select the projected version of “Connecticut Towns (County Subdivisions) - polygon features” from CT DEP in 1984 (the 5th entry from the bottom of this section). Be sure to select the polygon version. Download the zipped file named CT_TOWNS.1984.s24.ctdep.poly.zip to your newly created GIS folder.

For this project you will be working with data from the town of Middlefield.





Navigate back to the GIS Cyberinfrastructure Homepage: http://web2.uconn.edu/cyberinfra/module1/outline.html and download soils data “Data: Middlefield Soils”. Save the zipped folder to your data folder. Finally, download the quadrangle sheet (called a DRG) for the town of Middlefield from the course website (“Data: DRG”). This is an image (pixel-based) files with a .tif extension. Save the zipped folder to your data folder.

The Digital Raster Graphic (DRG) is a raster image, georeferenced to the UTM grid, of a scanned topographic map minus the map collar information. These are created by the United States Geological Survey (USGS). When you view these in ArcMap against the shapefiles you downloaded you will see that they are useful as a source or background layer. For example, they can be used to perform quality and accuracy tests on other digital files (assuming they are in the same projections!).



Be aware that while this is a projected coordinate system dataset, it is in NAD 27 CT State Plane, which is different from the other layers we downloaded (those are in NAD 83 CT State Plane or WGS 84). We will come back to this difference during the map manipulations. These image files are large and therefore take a bit of time to download. While you are waiting, ensure that all of your downloaded files are in your GIS folder. If they automatically downloaded to a location other than your GIS folder, move them to your GIS folder now.

Notice that the downloaded files have a .zip extension. This means that they are in a zipped or compressed format. The next step is to unzip them, which will create ArcGIS shapefiles (.shp) or raster files (such as the DRG which is .tif).

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The individual files contained within each zipped file can be viewed in Windows Explorer when you try to open the zipped files, but they will not be visible in ArcMap. You will need to extract all downloaded files:
Navigate to the GIS exercises folder you created.
The files that you downloaded and need to unzip are shown below.

The process for unzipping files may vary from computer to computer. Try the instructions below if you are unfamiliar with unzipping folders, but realize that on some computers you may need to open the zipped folder before extracting.
Right click on the first file and select “Extract All…” A screen similar to the one below should pop up or some variation depending on the version of your Operating System








The default will be to create a new, unzipped folder within your GIS folder that has the same name as the zipped file. Click Extract to extract the file. Repeat this process for the other zipped files. You will no longer need the zipped files, so you can delete them after successful extractions if desired. You should now have five extracted folders, one for each of the data layers (hydrography, roads, boundaries, soils, and the DRG).

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Using ArcCatalog ArcGIS shapefiles consist of a group of related files that are all required to reside in the same location on your computer to be displayed in ArcMap. The easiest way to ensure that all shapefile components remain together is to move or copy shapefiles in ArcCatalog.













Open ArcCatalog by going to your Program menu and selecting “ArcGIS”, then “ArcCatalog”. This should open a screen that looks like the one below. In the left-hand display, Navigate to your GIS folder containing the five data folders. In the right hand display, click on the “Contents” tab, then click on your GIS folder in the left-hand window to display its contents in the right-hand window. You should see the five data folders in the righthand display. Now double click on the Hydrography folder in either display window. You may see that this brings you to another folder within the primary folder. Double click this new folder if it appears and you’ll see 2 folders, one labeled “NAD 83” and the other labeled “WGS 84”. The data in this case is provided in 2 different datum (more on this topic later). For now, double click the WGS 84 folder. You should see 2 files—one line shapefile (indicated by the ), and one text file. Click on the line shapefile to select this file (it will be highlighted in blue) Click the “Preview” tab in the right-hand display. This will show you graphically what is contained in the layer if the “Geography” option in selected from the bottom dropdown menu. The table of data being used to generate the display will be shown if you select “Table” from the lower dropdown list in the “Preview” tab. Click the “Description” tab at the top of the right-hand display. You will see processing details for the data layer documented here.

Metadata is a critical component of geospatial data. It conveys to all users of the data the pertinent spatial parameters used for calculations and display and describes the history of the document, including input data and processing details. Geospatial data without metadata can be difficult or impossible for others to use, so careful attention should be paid to creating detailed metadata when creating new datasets.

Just to see how many files are going into the display of one shapefile, open Windows Explorer and navigate to your GIS folder and open the hydrography data folder. There are many more files displayed (with unfamiliar file types) than you see in ArcCatalog because all of these files are being used simultaneously to generate the shapefile display.

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In order to make multiple data layers easy to simultaneously add and manipulate in the associated mapping software ArcMap, we want to store as many as possible in a common folder.







Within ArcCatalog, display the contents of your GIS folder in the right-hand display Right click in your GIS folder and select “New” then “Folder” to create a new folder Name the new folder something like “Middlefield” In the left-hand display, navigate to the Hydrography line shapefile in WGS 84, right click, and select “Copy” In the left-hand display, right click on your new Middlefield folder and select “Paste” to create a copy of the hydrography layer in this folder. Repeat this process for the road (WGS 84), town boundary (WGS 84), soils, and DRG data.

You now have all of the data organized to begin your GIS project. Throughout this exercise, continue to try alternative choices to the ones simply specified in the directions. This will allow you to more fully explore the software capabilities of ArcGIS. Defining Spatial Reference Properties in ArcCatalog We know that the DRG uses a different coordinate system from the rest of the data we downloaded. In some cases, data are also delivered without all of the necessary spatial definitions embedded within the file, such as the projection, even if the information is known or provided in an associated document. This is the case for the DRG, so we will define the spatial projection for this layer in ArcCatalog.


In the left-hand display of ArcCatalog, right click on the DRG file (CDRG0067.TIF) and select “Properties”

This window displays all of the information about spatial references stored with the data. Scroll down and you will notice that the “Spatial Reference” section is blank or undefined. This is where projection information is stored; without this information, we will not be able to properly display and manipulate the DRG in ArcMap. We can define this information based on the definitions provided in the metadata file that came with your data download (DRGDOC.TXT).





Click on “Edit” next to “Spatial Reference” Click “Select”, then “Projected Coordinate Systems” We know from the metadata that the DRG is in NAD 27 CT State Plane, so select “State Plane” Select “NAD 27”, then scroll over to “NAD 1927 StatePlane Connecticut FIPS 0600.prj” and select this option 6






Click “Add”, then “OK, then “OK’ again to apply this selection to the DRG If you re-open the Properties for the DRG, you will see that the “Spatial Reference” information is now filled in to correspond to the NAD 27 CT State Plane projection. If you re-open the Properties for the DRG and see that the “Spatial Reference” was NOT updated to NAD 27 CT State Plane, you need to check your read/write permissions. To do this on a Windows OS, right click the folder containing the DRG and select “Properties”. Be sure the box is UNCHECKED next to “Read only” and click “Apply”. When prompted, select “Apply to folder, subfolders, and files” and click “OK”, then “OK” again to exit the Properties. Re-do the steps to define the spatial reference and this time they should be saved (be sure to check!).

Since ArcCatalog functions much like Windows Explorer (i.e., its function is file management), it can be closed at this time and all changes that you made will already be saved. Creating an ArcMap Project In ArcMap, you work within a “Data Frame”, which consists of data layers and tables. You can have multiple data frames per ArcMap project, though the default is to have one data frame. Only one data frame is active at a time and within that data frame you can have an endless number of datasets and tables. The currently active data frame is indicated by bold font of the data frame title. The project Table of Contents displays what data frames are available, as well as the data layers within each data frame. When you save a project, you are saving a snapshot of what you have open, and what is in the table of contents. The project file has the extension .mxd. Keep in mind that there are multiple versions of ArcMap; newer files are not backward compatible, so if you need to open a project created in an older version of ArcMap (e.g., open a file created in version 9.3 in version 9.2 on another computer), be sure to save the project using an older file type (options available are in a dropdown menu in the “Save a Copy” dialog box).



Start ArcMap: Start / Programs /ArcGIS / ArcMap You may see the following prompt. Select “Blank Map” and click “OK”.


You will now have a new project, with two primary display areas: table of contents (left panel), and the map view (right panel). The “toolboxes” panel can be accessed by clicking the of the screen. Dock the toolboxes panel on the right side of the screen.

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at the top

There are global environment settings applied to all functions used in the project. To view the global environment settings:
Right click in the “Toolbox” display area
Select “Environments…”. Environments set here will apply to all tools used in the project. Environments for individual tools can also be set when running that tool if the global settings are not appropriate for some reason.



Click on “Workspace” The default “Current Workspace” is a geodatabase where you installed ArcGIS, which means that geoprocessing outputs will be stored there. Change this file path to your current GIS working folder. Many geoprocessing tools also provide the option to save outputs to a specific location (which can be different from the input data folder).
If you specify a particular folder here, as suggested above, all geoprocessing outputs will be stored in the specified location. This may be useful if you want to have a folder that contains only derived data layers, for example.
The “Scratch Workspace” is where temporary files will be written during geoprocessing tasks. You are not likely to access these files, so you can specify a particular folder if you like, or leave the default.
Click “OK” to close the Environments dialog box. Adding a Data Layer A data layer is a representation of a class of similar features drawn within a data frame. Each data layer within the data frame has a legend that describes the features. Its attribute table can be queried to represent only chosen features. The data layer can also be restricted to a certain feature class for display.


Click on the Add Data icon

or select File  Add Data.

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Navigate to the correct directory and select the hydrography, road, and town boundary layers all at once. This is done by selecting the first data layer, and then while holding down the Control key, select the other layers. Add the full suite for the data frame by clicking “Add”.

Notice that the icons for each data layer represent the data type. Vector features are shown by points, lines, and polygons, respectively. Raster data are shown by a grid icon. To display layers in the map view simply click on the check box next to the appropriate data layer. By default all layers will be displayed when added.


Repeat the process to add the soils data. When you try to add these data, you will notice that you are presented with a warning message about differing coordinate systems:

Here, the data are provided in a different datum, which is system of fixed, very well known locations around the world used as permanent reference points for geolocation. The shapefiles we added previously are in World Geodetic System 1984 (WGS 83) and here we have data in North American Datum 1927 (NAD 27). Geospatial researchers have devised equations that allow data transformation from one datum to another, and we must employ one here to ensure that all of the layers we want to process are registered to the same coordinate system. As the warning indicates, differences among coordinate systems could lead to erroneous calculations.




Click “Transformations” Select “GCS_North_American_1927” from the list under “Convert from” Select “GCS_WGS_1984” from the dropdown list under ‘Into” 9






Select “NAD_1927_To_WGS_1984_1” from the dropdown list under “Using” Click “OK” to close the Transformations dialog box Click “Close” to accept the selections you just made and add the soils data to the map

This is a good time to save the project:
Select File / Save As /
Navigate to in the correct directory (your data folder) and name the file. The .mxd file extension will be added automatically and designates this as an ESRI ArcMap project file. Note: It is always wise to save your work periodically!

The layers will be displayed (stacked) in the order they are listed in the table of contents. If many layers are displayed at one, it may be difficult to see the details.


Experiment with moving layers around in the list to display the data in the most appropriate fashion. To do this simply click on a layer and drag it to the top of the list.

Adding Raster Data Recall that raster data is stored as a continuous surface of grid cells or pixels. An example of raster data is the DRG.


Navigate to the DRG file through the “Add Data” button and click “Add”

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Notice that ArcMap asks whether you would like to build “pyramids” for the DRG dataset. Pyramids are internal geometric constructs that allow faster zooming in and out in the map view of ArcMap. Select “Yes” and wait for a few seconds while the calculations are performed.




Now notice that you receive a coordinate system warning, just as you did when adding the soils data. Follow the same steps as you did for the soils data to transform the NAD 27 CT State Plane projection stored with the DRG to WGS 84 so that it is compatible with the other data we are using.

Renaming Data Layers and Frames It is often necessary to rename layers with the data frame and data frames themselves. In this case, for example, renaming the layers so that they do not have long, complex titles will make them more presentable. The point here is that ArcMap projects are often used in producing publishable maps, or are used directly in publication figures or in PowerPoint presentations.







Left click on a layer title in the table of contents twice (slowly) to highlight the name in a text box Type a new name for the layer Rename the layers as follows: CT_Roads_1984_s24_ctdep: Roads CT_Hydrography_1984_s24_ctdep_line: Hydrography CT_TOWNS_1984_s24_ctdep_poly: Towns CDRG0067.TIF: Middletown Quad Data frames can be renamed in the same way. Change the name of the data frame to “Middlefield Prime Farmland”

Zooming and Panning The Connecticut-wide data has a much larger extent (display area) than the layers representing only Middlefield. This is where the zoom and pan capabilities of ArcMap can come in handy. The zoom icons can be used in several ways: By clicking on a zoom icon, for example, and then dragging a box somewhere on your map view, your entire map will be zoomed in/out to the specified extent. The smaller the box, the more zoomed-in you will be, allowing you to see smaller features. This method gives you more control than using the fixed zoom-in or -out icons shown below because those tools will zoom to fixed amounts as opposed to wherever you click on the map view.

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The above buttons from left to right are: Pan (no zooming) Zoom to full extent Zoom-in (fixed amount) Zoom-out (fixed amount) Return to previous extent

These other icons are also used to zoom in and out. The zoom to full extent is convenient when you have layers from different geographical areas. For example, clicking on this in a view with Middlefield soils and Connecticut roads turned on would zoom so that both layers would be fully visible in the display. If you have zoomed in too far, the fixed zoom out will get you back to a recognizable extent while staying centered in the same place.

Creating a New Shapefile from Selected Features We want to create a boundary shapefile that represents only the town of Middlefield. We can accomplish this by selecting features from the Connecticut-wide Towns data layer and saving that selection as a new layer.




Turn off all layers except the Towns layer In the table of contents, right click on the layer name and select “Open Attribute Table” The attribute table for the layer will be displayed





Double click the “TOWN” column header. This will sort the data by town alphabetically. Scroll down to “Middlefield” and click the cell in the far left column (grey box) corresponding to that row. This will select the desired row and it will be shown highlighted in blue. Right click on highlighted row in the far left column and select “Zoom to Selected”. This will change the map display to show the selected town. Keep in mind that you can move the attribute table if it is in the way. In the table of contents, right click the Town layer again and select “Selection”, then “Create Layer from Selected Feature”. This will add a new layer file to the table of contents named “Towns selection” and it will be displayed in the map view. A layer file (.lyr) is a type of data layer that stores source data and data properties (i.e., it references another file, rather than being a standalone file).





Now we want to save this selection layer file as a new shapefile to use as a template for clipping data.

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In the toolbox window, select “Conversion Tools”, then “To Shapefile”, then “Feature Class to Shapefile (multiple). This will open a dialog box for the tool.




Select the new layer (Towns selection) from the dropdown list in “Input Features”. It will be added to the list below the dropdown list. Select the Output Folder by clicking the folder icon. Navigate to the folder where you want to save the new shapefile, then click “Add”. Keep in mind that you want the folder name to be displayed in the “Name” box, so you may need to navigate up to that folder from the default. The full file path will be displayed in the Output Folder box. Click “OK” Once the tool is complete, add the new data layer (follow “Add Data” process you completed above). The file name will be Towns selection.shp. Turn off all other data layers to see just the Middlefield polygon you just created. There will be two layers in the table of contents with the same name (Towns selection). The layer at the top of the list is the layer you just added (the new shapefile) and the second layer is the layer file that is dynamic and dependent on the selection from the Connecticut-wide Town layer. Delete the second layer in the list with this name (the dynamic layer file), leaving just the newly created shapefile, by right clicking on the layer file in the table of contents and selecting “Remove”.










Extracting Data We can now “clip” or crop the data from the other Connecticut-wide data using the Middlefield template you just created. Clipping has two benefits: 1) your presentation maps will not include extraneous data and 2) your file size will be smaller (assuming you remove the larger scale data files after the clipping, of course).






In the toolbox display “Analysis Tools”, then “Extract”, then “Clip”. This will open a dialog box for the Clip tool. Select the Hydrography layer from the dropdown list of Input Features. Select the Middlefield shapefile you created from the dropdown list under Clip Features. Set the file name and file path for the output by clicking the button next to “Output Feature Class”. Save the file in your “Middlefield” folder and name the file Middlefield_hydro" Leave the XY tolerance blank and click “OK” to run the tool. 13







The new, clipped hydrography layer will be added to the table of contents automatically and will be displayed in the map view. Repeat this procedure for the roads and soils layer. You now have 4 data layers just for Middlefield: the town boundary, hydrography, roads, and soils. Rename the new layers to: Middlefield Town, Middlefield Hydrography, Middlefield Roads, and Middlefield Soils (see earlier instructions if you forgot how to do this).

Creating Data There will inevitably be occasions where the data you want is not available because it has never been created. ArcCatalog and ArcMap allow you to create your own shapefiles through a process called onscreen digitizing.


In the map display, turn on the Middlefield Town and Middletown Quad layers. Click on the zoom in icon




and drag a box around the designated area as shown below.

Adjust your window so that you can see Beseck Lake as displayed below. You may need to turn off layers other than “Middletown Quad” to see the DRG labels. 14

There are several lakes found throughout Middlefield. Using ArcMap’s on-screen digitizing capabilities you will digitize, and therefore create, a shapefile of this lake. However, before we can add new features, we must create a new shapefile to store those features. We can create new shapefiles in ArcCatalog.










Open ArcCatalog and navigate to your GIS folder. Highlight the folder in the left-hand display. From the “File” menu, select “New”, then “Shapefile”. A dialog box will appear where you will set the attributes of the new shapefile. Name the new layer “Lakes” under “Name:” Lakes are typically (and logically) represented by polygon features. Select “Polygon” from the dropdown list for “Feature Type” The spatial reference should be set to match the layer that we are digitizing features from. In this case, we are digitizing lakes from the Middletown Quad, which is stored in NAD 27 CT State Plane. Set the new “Lakes” shapefile to have this same spatial reference (refer to your earlier instructions if you need a reminder on how to do this) Click “OK” to create the new file according to your specifications Close ArcCatalog

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Now that you have created the empty shapefile, add it to your project in ArcMap. You will again have to set the transformation parameters to display the NAD 27 CT State Plane file on the same map as the WGS 84 data (hint: refer to earlier instructions). Open the attribute table of the Lakes layer in ArcMap (hint: right click on the layer in the table of contents). Notice that there are no features stored in the dataset. Close the attribute table

Adding to the shapefile requires editing the layer. By default ArcMap is not in editing mode; this prevents users from inadvertently making permanent changes to datasets. Here, we will activate editing to digitize Beseck Lake.



Click the button to open the editor toolbar Click the “Editor” button and select “Start Editing”


You may see a warning message that some layers’ spatial references do not match the dataframe. We already know this from when we added the data layers to the map (recall that those were the layers in NAD 27). This message reminfs you that using data with different coordinate systems must be done with caution! Select ‘Continue”.
You should see a “Create Features” and “Construction Tools” panel on the right side of the screen. Click the “organize templates” button in the “Create Features” panel.
In the “Organize Feature Templates” dialog box that appears, click “New Template”


In the “Create New Templates Wizard”, select “Lake”, then click “Finish”
The layer “Lake” should now be visible in the “Organize Feature Templates” box. Close the “Organize Feature Templates” dialog box
You can now select the “Lake” layer to edit. You can see the “editable” layers in the Editor panel on the right side of the screen. Highlight the “Lakes” shapefile in the “Create Features” panel. Select “Polygon” from the “Construction Tools” panel.

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Click on the edge of Beseck Lake in the map display. Each time you click, the point will become an anchor, or a point that defines the polygon. Continue to click on the lake edge to create the polygon outline. Smaller distances between anchor points yield more detailed polygons. When you are very close to completing the polygon, double click where you want the anchor point. This will set the last anchor point and automatically close the polygon feature.

You must save your edits!! From the “Editor” dropdown list, select “Save Edits” When you are finished editing, select “Stop Editing” from the “Editor” dropdown list. Open the “Lakes” attribute table. You should now see one polygon in the table.

It is often desirable to include attribute information to each polygon feature in a dataset. We can add this information to the “Lakes” dataset once the features are created. 17

















From the toolbox display, select “Fields” from the “Data Management Tools” Select “Add Field” Select the “Lakes” shapefile from the “Input Table” dropdown list Name the new field “Name” under “Field Name” Select “TEXT” as the “Field Type”. The many types of fields that can be used are described in the right-hand help screen in the “Add Field” tool. Click “OK” to run the tool

Open the attribute table for the Lakes shapefile. There is now a blank field for Name that we can populate. Select “Start Editing” from the “Editor” tool dropdown list. In the Lake attribute table, click in the cell we want to fill under the “Name” field so that the cursor is blinking Type “Beseck Lake” in the cell In the “ID” field, enter “1”. This will allow you to give every polygon you create a unique ID number Select “Save Edits” from the “Editor” tool dropdown list, then select “Stop Editing”

Congratulations, this concludes the first part of this exercise. Save your work and continue to part two.

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Part II: Locating Prime Farmland in Middlefield Important Topics Covered • • • • • • • •

Examining the Attributes of Map Features Displaying Specific Fields Creating an Effective Representation of the Data Using the Dissolve Function Using the Buffer Function Using the Intersect Function Using the Union Function Exporting the Map

Examining the Attributes of Map Features In order to understand the features on the Soil layer you must look at the table where this attribute information is stored.




Ensure that the Middlefield Soils layer is turned on (box is checked in table of contents) Open the attribute table for the Middlefield Soils layer (see instructions from Part I) Resize the table window so that more fields (columns) are visible

Each attribute table is comprised of rows (termed records) and columns (termed fields). Each record represents a feature in the layer. Each field stores attribute information about a particular record. The relationship between records and the features in the layer allow information to be selected in the layer. Someone has already created a field called “Farmland” that classifies the various soil types according to their agricultural productivity. You will create a map that displays this information. Displaying Specific Fields It may be necessary or desirable to change which field of an attribute table is used to display the data in the map view. This is easily defined and changed using the layer “Properties” window.







Close the Table Open the layer Properties for Middlefield Soils by right clicking on the layer title in the table of contents and selecting “Properties” Among the tabs in the Properties window, select “Symbology”. This tab allows you to change how the data are displayed on the map. From the “Show” menu on the left side of the window, select “Categories”, then “Unique Values”. Select “FARMLAND: from the “Value Field” dropdown list, then click “Add All Values” at the bottom of the window. This will add all of the values from the “FARMLAND” field to the main display window. Make sure the box next to “” is unchecked, then click “OK” to change the map view.

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Creating an Effective Representation of the Data










The colors can be changed one-by-one by right clicking the colored box in the table of contents and selecting a new color from the displayed palette. Additional color and fill options can be accessed by double clicking (left click) on each colored box in the table of contents (this opens the “Symbol Selector”). Among the available options are additional fill colors, the color and width of the polygon outline line, and fill patterns. The easiest way to change individual fill patterns is to choose an option by scrolling to the bottom of the left-hand display window in the Symbol Selector. Click “OK” once your selections are complete. To change the overall color scheme for the entire layer, again open the Symbology tab in the layer Properties window (hint: instructions above). Select a new color scheme (such as a pastel color scheme) from the “Color Ramp” drop down menu. To change the outlines of all field values on display, right click on any colored block in the main display window of the Symbology tab and select “”Properties for All Symbols…”. In order to better see the blocks of similar soil types, select “No Color” for the Outline Color and click “OK”. Click “OK” to save the changes you made in the Symbology tab. In this case, we want to highlight areas of Prime Farmland. Change the color for this Soil Type to bright yellow. Change the other soil types to grey. Line colors and widths can be changed using the same methods. Increase the line width for the Middlefield Roads to 2 to make the roads more visible. Change the names of each soil type within the Middlefield Soils layer using the same methods you used to rename the data layers and data frame (Part I):

Not Prime or Not Statewide Important Farmland Soils  Additional Statewide Important Soils  20

Not Prime Farmland Soils Not Prime Farmland Soils

 

Prime Farmland Soils Water

Prime Farmland Soils Not Prime Farmland Soils

You now have a map of farmland soils in Middlefield with the location of prime farmland soils highlighted. This was achieved by manipulating the graphic display as opposed to actually altering the data in the table. In the next section, you will achieve the same results but this time by altering the attribute table.

Using the Dissolve Function You will now create a new shapefile that displays each of the categories as one polygon by dissolving the boundaries of like attributes in order to discern Prime Farmland Soils from Non-Prime Farmland Soils. Dissolving the polygons to achieve the desired effect is a two-step process.






From the toolbox display, select “Data Management Tools”, then “Generalization”, then “Dissolve”. Choose Middlefield Soils from the dropdown list of Input Features The Output Feature Class will be automatically filled in, with the output file saved in the same folder as the input data. As always, this can be changed if desired. In the “Dissolve_Field(s) (optional)” list, check “FARMLAND” Leave all other defaults and click “OK” to run the tool.

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The result of the Dissolve tool will be automatically added to the project. Rename the new layer “Aggregated Farmland” and change the display to show the four categories of farmland (hint: instructions above!).

Notice that the Dissolve tool did not dissolve the layer into “Prime Farmland” and “Not Prime Farmland” but instead into the original categories. This is because the changes in the representation of the data were changes to the graphic display as opposed to physically altering the data. However, contiguous polygons within the prime farmland category now have been dissolved into larger polygons. You will now alter the data so that using the Dissolve tool will create a shapefile that allows you to display one polygon of prime farmland and one polygon of non-prime farmland.









Open the Aggregate Farmland attribute table Click “Editor” on the Editor toolbar and select “Start Editing” A warning dialog box may appear that warns against editing maps with datasets in different coordinate systems. While this is a useful caution, we know that the data we are editing is all in the same coordinate system, so click “Continue”. In the “Aggregate Farmland” attribute table, click on the cell containing “PRIME FAMRLAND SOILS” to make the text editable Change the name of “PRIME FAMRLAND SOILS” to “PRIME FARMLAND” Change the names of all other entries in the FAMRLAND field to “NOT PRIME FARMLAND” From the editor toolbar dropdown menu, select “Save Edits”, then “Stop Editing” Save your project!

It should be apparent at this point as to why this is a two-step process. If you had tried to re-code the original Middlefield Soils table it would have taken a long time given that there are a substantial number of records. In the table resulting from the dissolve tool you only have to enter data for four records.


To refresh the table of contents display to reflect the changes in the attribute table, go to the Symbology tab in the layer Properties menu and click “Add All Values” again. You should now see only two categories in the Aggregated Farmland layer. Change the colors to grey and yellow and remove the polygon outlines. 22

You have now located and effectively displayed prime farmland in Middlefield. Using the Buffer Function You will use the buffer tool to further isolate areas of ideal soils, by creating a buffer zone around them. This will be done by buffering the Middlefield Roads layer to subtract farmland areas that are within 200 feet of the roads. It may be important, for example, to maintain some sort of buffer or safety guard to prevent the surface discharge from motor vehicles from flowing off roads, seeping into the soils and potentially contaminating the crops.



Turn on the Middlefield Roads layer Change the road line width back to 1 by double clicking the line in the table of contents.

To buffer the roads:
From the toolbox display, select “Analysis Tools”, then “Proximity”, then “Buffer”.
Select “Middlefield Roads” from the dropdown list of Input Features. As usual, the Output Feature Class will be automatically determined and can be modified if desired.
Chose “Linear unit” for the “Distance” metric. Set the buffer distance to 200 and select Feet from the dropdown list. Note that many linear units are available. If the units selected are different from those native to the layer, ArcMap will convert the distances “on the fly” when running the tool. Another option is to reproject the data layer into the proper units before running this tool to provide you with more direct control over the geoprocessing. Changing datum and projections can be complex and will not be covered in this course segment.
Select “All” from the dropdown list for “Dissolve Type (optional)”. This will prevent overlapping buffers.
Leave all other defaults and click “OK” to run the tool. The resulting shapefile will be automatically added to the project.

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Rename the new buffered road layer “Buffered Roads” Zoom into an area where the road crosses Prime Farmland in order to see the buffered area more clearly. Do this by clicking on the zoom-in icon and dragging a box around a smaller area.

Using the Intersect Function You will now use the intersect tool to create a layer that exhibits the attributes of both the soils data and the buffered roads.


From the toolbox display, select “Analysis Tools”, then “Overlay”, then “Intersect”.

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Choose Aggregated Farmland and Buffered Roads from the Input Features dropdown list. As usual, the Output Feature Class is automatically determined and can be changed if desired. Leave all other defaults and click “OK” to run the tool. The result will be automatically be added to the project.

Rename the new layer Intersection of Roads and Farmland. Change the display of the new layer in the Symbology tab. Select “Categories”, then “Unique Values” and chose “FARMLAND” for the Value Field. Click “Add All Values” and you will see Prime and Not Prime Farmland displayed. Change the colors to grey and yellow as done previously. Click “OK”. Using the zoom-in tool, display an area so that you can clearly see the results of the intersect function.

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Using the Union Function You will now use the union function to create a new layer of the buffered areas and the farmland soils.








From the toolbox display, chose “Analysis Tools”, then “Overlay”, then “Union”. Select Aggregate Farmland and Buffered Roads from the Input Features dropdown list. As usual, the Output Feature Class is automatically determined and can be changed of desired. Leave all other defaults and click “OK” to run the tool. The result will be automatically be added to the project.

Rename the new layer “Union of Roads and Farmland” and change the display to reflect Prime and Not Prime Farmland as done previously. Using the zoom tool, display an area so that you can clearly see the results of the Union function.

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You have now identified the most suitable land for farming and the land within 200 feet of the roads. With such a close proximity to the roads, this land could contain contaminates such as motor oil, gasoline and other automotive pollutants. Thus, the most suitable farmland would be that which is classified as prime farmland and located 200 feet from the roads. Here we are going to select portions of the layer to show only the features that we feel are desirable.













From the “Selection” menu, chose “Select by Attributes” Chose “Union of Roads and Farmland” from the Layers dropdown menu and select “Create new selection” from the “Method” dropdown list. Double click on " "FID_CT_Roa" from the list of available fields. This name will appear in the lower display box. Click “Get Unique Values” to see the available values that can be selected upon. Click the “=” button, then double click “-1” to indicate that you want to select areas outside of the buffer area. Click “AND” to add another selection criterion Double click “FARMLAND” to add it to the lower display box, then click “Get Unique Values” again. Select “=”, then “PRIME FARMLAND” to indicate we want to identify only areas of prime farmland outside of the buffer area. Click “OK” to run the tool. The selected areas will be outlined in blue in the map display.

Create a new layer from the selected features (hint: right click on the Union of Roads and Farmland layer name in the table of contents to begin, see Part I). Convert this new layer to a shapefile and add it to the map manually (hint: use a Conversion Tool, see Part I). Rename the new shapefile to “Prime Farmland 200 feet from Roads” and change the display to represent Prime Farmland outside of the 200 foot road buffer in yellow. Since the yellow may be difficult to see on a white background, add a grey outline of weight equal to 1. Turn on the Middlefield polygon you extracted in Part I. Change the display to no color for the fill and a grey outline.

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You now have a thematic map of prime farmland in the Town of Middlefield buffered by 200 feet along all roads. Exporting the Map Now let’s try making graphics from this exercise that could be printed or inserted into publications. Note that print copies may be in black and white, so in making an effective map, you may want to go back and change colors or use shading to make for a more effective map. You can export the map in two ways: This first is quick and easy. Simply export your view by going to File and Export Map. There are a few file type export options. Many of the file types are compatible with other commonly used software (such as Microsoft Word). A good choice is TIFF (.tif) if you don’t have a personal preference and the file isn’t too large; if memory is limiting, select a more compressed format, such as JPEG (.jpeg). The second option is to produce a more formal, publication quality map. Go to the “View” menu and select “Layout”. This will change your map to layout view and apply a basic template. The layout tools are a specific toolbar that is typically displayed by default, but may be displayed at the top or bottom of the screen. If you are not sure if the toolbar is displayed, you can check by selecting “View”, then “Toolbars”, and ensuring the layout toolbar is checked. You will likely want to display a legend, compass rose, and scale in addition to a map title. You can achieve this by selecting a premade template. Click the “Change Layout” icon , then select the “General” tab to display available design templates. “LetterPortrait” contains all basic map elements. Click “Finish” after highlighting the desired template. A title can be added by double clicking in the area specified. Other elements (e.g., the legend) can be moved to a more readable location by clicking and dragging the element in the display.

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Each element can be edited individually by double clicking it. The scale bar, for example, will be displayed in the map units by default (feet, in this case), but can be changed by double clicking the scale bar and choosing the desired units from the “Division Units” dropdown list in the “Scale and Units” tab. Other easy changes are the style of the scale bar and the compass rose. Explore the many customization options for making the display aesthetically pleasing. When you are finished, select “Export Map” from the File menu. For additional practice and exercises using Arc, you might also try some of the free on-line training tutorials on ArcMap by going to the ESRI site: http://campus.esri.com/ For background and an introduction to GIS, go to http://www.gis.com/ and look at: What is GIS? Why use GIS? What can you do with GIS?

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