Introduction to Geography, GIS, spatial data and use of GIS in health ...

Introduction to Geography, GIS, spatial data and use of GIS in health & ArcGIS Lex Comber University of Leicester [email protected]

Aims • To introduce the importance ofGeography (space and places) and spatial analyses • To illustrate some types of Spatial Data – Content&Format

• To show how GI can be analysed in a GIS • To introduce the ArcGIS software package

Geography • GIS is a Geographical Information System – What does this mean?

• Computer software for analysing Geographical Information – What is Geographical Information? – How does it differ from other information?

• ‘Geographic’ and ‘Information’ – Geographic: it has a spatial component (location) – Information: it tells us something about that place (attribute)

• This is one of they aspects of geographic data • Most data is collected somewhere NB: I will use the terms “spatial data” and “geographic information” interchangeably

Geography • Most data is collected ‘somewhere’ • Now the sources of GI (and the volume of GI) is increasing – – – –

Mobile Phone, Smart phones Credit card use Twitter Web 2.0( is that 2.Old now?) – flickr, google maps

• The number of types of applications using GI is also increasing – – – –

Google Maps, Directions, Sat-Nav, Web mapping, Marketing (e.g. supermarkets) Remote Sensing, GPS enabled devices

Geography • Have any of you used a GIS? • I would say that you may use one everyday without realising! – Directions, web-mapping etc – Deliveries are scheduled to Lawson Station / 7Eleven etc with a GIS

• And…spatial data is everywhere

Spatial Data is everywhere!

Spatial Data is everywhere!

Spatial Data is everywhere!

Haiti – Open Street Map (‘before’)

Haiti – Open Street Map (‘after’)

Spatial Data is everywhere!

Spatial Data is everywhere

Geography • GIS can be used to analyse the spatial relationships • Tells us what happens where • Allows us to link spatial pattern to process

Geography • GI has a location and attribute – What is so special?

• Tobler’s Law: "...the first law of geography: everything is related to everything else, but near things are more related than distant things.” (Tobler, 1970) • Can anyone think of some obvious (non-health) examples? – Housing type, unemployment, habitats, etc etc

• Objective is to identify clusters of similar events in space (& maybe time) – Implies some statistical analysis of attribute and location

• Used to identify and visualise clustering

Nakaya, T. (2010): ‘Geo-morphology’ of population health in Japan: Looking through the cartogram lens. Environment and Planning A 42(12)

Geography • Key message: space is important – Not all things happen in the same way in all places – Geographical analyses allow us to explore the spatial relationships in phenomena – GIS allows to develop these analyses

Spatial Data • In general spatial data comes in one of 2 formats – Raster: a continuous surface of gridded cells – Vector: collections of discrete objects

• They can both be used to represent any spatial features but have their own characteristics • Most analyses use either Raster or Vector but generally not both

Spatial Data • Conceptualising the Earth • 2 fundamental ways of representing geography

Spatial Data: Raster • Continuous fields – Grids, cells, images,

• For each object – Geometry – Attributes – Held in a single table – Eg ascii header

Spatial Data: Raster

Spatial Data: Raster • • • • • •

ncols 5279 nrows 4010 xllcorner 234582.3 yllcorner 751431.9 cellsize 25 NODATA_value -9999

• Single theme • Geometry is implicit from – X, Y corner – Cols & Rows – Cell size

Spatial Data: Raster • Selection of raster grid size is important Fine raster

Coarse raster

Spatial Data: Vector • Points, Lines, Areas • Discrete points (nodes), lines (arcs) and areas (polygons) used to identify locations • Positions of objects: identified by sets of Cartesian (XY) co-ordinates X A Y

Points

Lines

Areas

Spatial Data: Vector • Vector example: areas – Lines captured as series of points – Curves approximated by differing density of points – Areas captured as series of points (vertices) connected by straight lines – Areas called polygons, patches, parcels

1

3 2 4

Point number

x,y coordinate

1

2,8

2

4,6

3

8,7

4

6,3

Line number

x,y coordinates

1

1,6 3,5 6,7 7,3

2

1,2 3,1 6,5 7,7

Polygon number

x,y coordinates

1

2,4 0,8 2,8 7,8 7,6 5,5

2

5,1 3,3 6,4 9,3 7,1

1

Storing coordinates for different feature types 2

Spatial Data: Vector • Key advantage of vector data: – Object level attribute – Linked to database which may have many fields – Allows MULTIPLE attributes

Spatial Data: Summary • 2 main ways of representing geography (Data Models) • Vector: Discrete objects – – – – –

Objects with well-defined boundaries in empty space Objects can be counted Identified by their dimensionality Expressed as series of tables Poor for continuous data

• Raster: Continuous fields – Represents the world as a finite number of variables, each one defined at every possible position – Represents what varies and how smoothly – Good for surfaces such as DEMs

Spatial Data: Summary

x,y x,y

x,y

Raster or Grid uses cells to model reality

Reality

x,y

x,y

Vector discrete representations

x,y

Non-agricultural land

Comber et al., (2008). The creation of a national agricultural land use dataset: combining pycnophylactic interpolation with dasymetric mapping techniques. Transactions in GIS 12(5)

…the story so far… • I have talked about Geographic Information – Location, Attribute

• We have looked at different data formats – Raster, Vector

• Now, we will consider how such data can be analysed in a GIS

GIS Analyses • Formalizing the analysis model is the most important part • We use GIS to analyse spatial data… • BUT both…the data, and the analysis of that data need to relate to some process, some hypothesis or some model, etc in terms of – Relationships, functions, data manipulations

GIS Analyses • Formalizing the model is the most important part • Example of expected links: – Public Health and Land Use – Deprivation and lung cancer – Sanitation and Disease frequency (eg cholera) • John Snow, 1854

– Was this the first GIS?

GIS Analyses • John Snow • London (Soho) • 1854

GIS Analyses • Dr John Snow – the first spatial detective • Identified the source of cholera in 1854 • Plotted cholera cases in and around the West End / Soho in London • Identified contaminated water pumps • Later collated by other workers http://www.ph.ucla.edu/epi/snow.html http://www.ph.ucla.edu/epi/snow/mapsbroadstreet.html

GIS Analyses • In spatial analyses the aim is to link spatial pattern to some process – This may involve investigative work to determine the process – Or the process may have been identified by other work (papers in the literature, earlier research, hypotheses testing) – Can you think of any public health examples?

• This is usually done through some formal model

GIS Analyses • The model specifies factors that contribute to the solution – Rural Areas  Old population  more EMS (emergency) cases – Factory  pollution  worse public health – Deprivation  more Smokers  child Asthma

• Data is needed for each factor in the model • In a GIS data needs to be spatial data • We can think of these as data layers

GIS Analyses • GIS allows spatial to be ‘queried’ Layer_1 = ‘high’ AND 0.3 < Layer_2 < 0.7 AND Layer_3 = ‘good’ OR Layer_ 3 = ‘very good’ • We can consider these as set operations • We use these when we combine data in an overlay procedure

Query

GIS

GIS Analyses • Set operations (blue area) – AND – both conditions are true – NOT – one of the conditions is false, the other is true – OR – one of the conditions is true – XOR (aka ‘NOR’): just one of the criteria but not both

AND NOT OR XOR

GIS Analyses • Vector – ‘Object view’: the world represented as an empty space with discrete entities (e.g., forest, city, lake, road) within it – A vector model indicates where everything occurs - gives a location to every object

• Raster – ‘Field view’: the world represented by continuous variables in separate layers e.g., elevation, soil type, population density – A raster (grid) data model indicates what occurs everywhere at each place in the area

ArcGIS • There are many GIS software – ArcGIS is one of the industry standards – Others include • MapInfo • Idrisi • Quantum GIS

– They all have their own advantages – You can do everything in each fo them, but often through different routes

ArcGIS • ArcGIS contains a series of different modules – ArcMap, ArcCatalogue, ArcView – Have a look at the documentation / help files to find out what they do

• We will be working with the ArcMap module • When you open ArcMap you are presented with a series of panels in the window

ArcGIS

ArcGIS

ArcGIS

ArcGIS

Finally • This session has – Described importance of geography – Shown the 2 main ways of representing geographical features – Introduced some of the principles of spatial analysis in a GIS – Shown a few screen grabs of ArcGIS

• The practical session will introduce you to GIS and spatial analysis in a GIS

References •

Good general GIS text – Longley, P.A., Goodchild, M.F., Maguire, D.J., Rhind, D.W., Geographic Information Systems and Science. (2005 2nd ed/ 2010 3rd ed), John Wiley & Sons Ltd

•

Health GIS – Ric Skinner, (2010). GIS in Hospital and Healthcare Emergency Management, CRC Press ($99.95, €81.99, £63.99 - library) – International Journal of Health Geographics http://www.ijhealthgeographics.com/

•

Scientific references – Goodchild et al. (2007). Towards a general theory of geographic representation in GIS, International Journal of Geographical Information Science, 21(3): 239–260 – PS: if you want to browse and download Goodchild’s other papers, you can http://www.geog.ucsb.edu/~good/papers/