introduction to geography, gis, spatial data and …€“ arcmap, arccatalogue, arcview – have a...

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!


Haiti – Open Street Map (‘before’) Haiti – Open Street Map (‘after’)

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


• 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


• 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


• 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


• 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

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/

http://www.ij-healthgeographics.com/�

http://www.ij-healthgeographics.com/�

http://www.geog.ucsb.edu/~good/papers/�

introduction to geography, gis, spatial data and …€“ arcmap, arccatalogue, arcview – have a...

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