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Introduction to Geography, GIS, spatial data and use of GIS in health & ArcGIS
Lex Comber
University of Leicester
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
Y
X
Points Lines
A
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
2
3
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 7,11
2
Storing coordinates for different feature types
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
Vectordiscrete
representations
x,y
x,y
x,y
x,yx,yx,y
Raster or Griduses cells to model
reality
Reality
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)
Non-agricultural land
…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.htmlhttp://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 < 0.7AND
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
OR
NOT
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.ij-healthgeographics.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/