Geographic Information Systems (GIS) allow users to store, visualize, and analyze spatial data in digital formats. GIS can be used to ask questions about the location of things, what happens at locations, and how things are spatially related. Spatial data can be represented using vector models of discrete data like points, lines, and polygons, or raster models of continuous data like elevation or land cover which have no clear edges. Real world entities may have both discrete and continuous qualities, and different GIS data structures are suited to representing each type of data.

1. Digital models of the landscape:
Geographic Information Systems (GIS)
A fragmented world or a smooth
world?

2. What is GIS?
• GIS-Geographic Information Systems
• Computerised information systems
designed to handle geo-spatial data
– data which relates to location in the
world

3. The capabilities of GIS
GIS gives users powerful capabilities :
• to capture and store spatial data in digital formats (data
models)
• to visualise spatial data and relationships (geographical
models)
• to ask questions based on that spatial data (data querying
and spatial analysis)

4. Prime GIS capability: asking spatial questions
• GIS lets us ask questions about the
location of things

5. Prime GIS capability: asking spatial questions
• GIS lets us ask questions about the
location of things
– Questions about where things happen
Where are there trees of this type?

6. Prime GIS capability: asking spatial questions
• GIS lets us ask questions about the
location of things
– Questions about where things happen
– Questions about what happens at a
location
Where are there trees of this type?
What is the GDP of this country?

7. Prime GIS capability: asking spatial questions
• GIS lets us ask questions about the
location of things
– Questions about where things happen
– Questions about what happens at a
location
– Questions about how things are related
spatially
Where are there trees of this type?
What is the GDP of this country?
How far across the ocean?

8. Where were there more than 40 FMD cases up to Mar 18, 2001?
FMD>40?
Questions about where things happen

9. Where were there more than 40 FMD cases up to Mar 18, 2001?
FMD>40?
Answer in purple
Questions about where things happen

10. When was FMD first recorded in Gloucestershire?
Questions about what happens at a location

11. Which towns are in Gloucestershire?
Questions about how things are related spatially

12. GIS capability: visualising spatial data and relationships
• Data is stored in structured databases
• GIS is used to make spatial data and patterns in
data visible
• This visualisation can be in the form of maps,
charts or reports
• These are all models of reality

13. Applications of GIS in Property and Rural Development
• Monitoring land use change
• Property portfolio management
• Land classification
• Property value maps
• Accessibility mapping
• Agricultural monitoring
• Environmental impact assessment

14. Land use change Aerial photograph mosaic: 1972

15. Land use change Aerial photograph: 1995
Changed
field patterns
New woodland
New road
New houses

16. Rural Property management

17. Rural Property management
B
A

18. Rural Property management
B
A
ID farm_name tenure rent_year owner type area
1 Farm A annual lease annual George dairy 467
2 Farm B perpetual lease none George dairy 456
3 Farm C 10 year lease 2006 Henry beef 367
4 Farm D 10 year lease 2003 Thomas arable 678

19. Land classification from Satellite images
Data from Idrisi Project

20. Accessibility mapping
rural travel times: before Hurricane Mitch (1998)
Source: CIAT -
World Bank -
UNEP Indicators
Project, November
1998.
Map source:CITA
1998 Government
of Honduras
(SETCO) 1998, La
Prensa Managua
Travel Time 1998, La Prensa
Graphica San
30 Minutes Salvador 1998 .
1 Hour
2 Hours
4 Hours
8 Hours
16 Hours
2 Days

21. Accessibility mapping
rural travel times: after Hurricane Mitch (1998)
Source: CIAT -
World Bank -
UNEP Indicators
Project, November
1998.
Map source:CITA
1998 Government
of Honduras
(SETCO) 1998, La
Prensa Managua
Travel Time 1998, La Preensa
Graphica San
30 Minutes Salvador 1998 .
1 Hour
2 Hours
4 Hours
8 Hours
16 Hours
2 Days
Damaged Bridge

22. Agricultural monitoring
Crop “C”
area 38 ha
Crop “B”
area 34 ha Vector farm map
laid over raster
satellite image
Crop “A”
area 25 ha

23. Environmental impact assessment

24. Environmental impact assessment
Historic site
Protected river
Ancient forest
Environmentally
sensitive zones

25. Environmental impact assessment
Historic site
Protected river
Ancient forest
Environmentally
sensitive zones

26. Building a model: components, principles and rules
• All models are built of components
• When combined according to set
principles and rules they create the
model (vector and raster model rules)
• The components contain data about
reality
• That data can be described as discrete
or continuous
• Discrete and continuous data models
show the World in very different ways

27. How computers store spatial data structures
• Vector structures are used where real-
world objects need to be mapped.
– Discrete data models
– The fragmented view of the World
• Raster structures are used where
continuous “fuzzy” data must be mapped
– Continuous data models
– The smooth model of the World
• (Refer back to earlier unit on digital
mapping)

28. Discrete data: things with edges - fragments
• Vector model
• Fragments are things with edges…
– A point has an edge of zero length
– A line has an extensive edge, with a
starting point and end point
– A polygon has a closed extensive edge,
with no starting point or end point
– All discrete spatial data models represent
the World with graphic points, lines and
polygons
– Similar to a paper map...

29. Contrasting a vector models with traditional cartography
Paper map: Everything is
drawn using points, lines and
polygons. But they are just
drawings. They have colour,
texture, density etc. but no
intrinsic information about the
real world objects they
represent
Digital vector model: points, lines and
polygons, but each is defined by its
geographical co-ordinates and is linked to
data about the real world object it
represents. Colour, line thickness etc can
all be changed without changing the actual
data intrinsic to the model

30. The vector model as a representation of discrete data
Tenancy Crops
Land units polygons:
Each map has different colouring
to represent different sets of data
we want to study.
Land cover

31. Examples of discrete spatial data
• Political boundaries
• Buildings
• Land parcels
• Roads
• Electricity pylons
• Rivers (?)
• Farm fields (?)

32. But: how discrete are real world entities?
Is there an
edge
here?
Where
exactly is
the edge
of a
forest?

33. Continuous data: things with no edges – smooth surfaces
• Raster model
• Some things exist wherever you choose to
measure them
– Every point on the land has a height above sea
level
– Every place in the atmosphere has an air pressure
– Every piece of land has some sort of land cover
• These are examples of continuous data and
they are difficult (impossible?) to model. The
raster data model is one attempt to do this.

34. Continuous data structures: how raster data is displayed
Whole region is divided
into equal sized cells
Each cell holds one
value (attribute)
Attributes can be
represented by colours

35. The raster model as a representation of continuous data
One cell
The model consists of a
complete matrix of cells, all
of the same size, each
with a single value which is
represented visually by a Colours show height
ramped colour Each cell is assigned one
height measurement,
which may be the
maximum, minimum,
median, or mean height of
the ground in the cell

36. Raster models aren’t really continuous at all…
How the data is
visualised as a raster
• When we create the raster grid, we are
dividing the World into discrete cells and
assigning single values to each. There
is a hard, discrete boundary around
each cell-fragments
• Are there any genuinely continuous
data models?
– They are working on it, warped surfaces
and TINs (triangulated irregular networks)
are possibilities but they have their own
problems.

37. Classifying continuous data: the influence of break points
“Continuous” height information

38. Classifying continuous data: the influence of break points
“Continuous” height information Classified into 1m bands

39. Classifying continuous data: the influence of break points
“Continuous” height information Classified into 1m bands
Classified into 5m bands

40. Classifying continuous data: the influence of break points
“Continuous” height information Classified into 1m bands
Classified into 5m bands Classified into 10m bands

41. Converting vector  raster

42. Converting vector  raster
Data can be degraded,
unpredictably and
irreversibly every time you
convert from one data model
to the other

43. Converting vector  raster
Data can be degraded,
unpredictably and
irreversibly every time you
convert from one data model
to the other

44. What GIS programs are available
• Large number of GIS programs on the market
– Some are very specialised for scientific purposes
– Some are little more than digital map viewers used
in asset management
• Main systems used:
– ArcGIS from ESRI Inc.
– Idrisi from Clarke University
– Geomedia from Intergraph Inc
– MapInfo
– Small World

45. RAC GIS systems
ArcGIS from ESRI
Installed in room 10