2. Why do we need models?
The real World is too complex to
manage in its entirety. Models
give us a simple manageable
representation
A map gives us a simple
model for studying what we
are interested in
3. Maps: what they are, what they show
• Map: a representation, by graphical means,
of selected features of the Earth
– A map is a scale drawing of only a selection of
features
4. Maps: what they are, what they show
• Map: a representation, by graphical means,
of selected features of the Earth
– A map is a scale drawing of only a selection of
features
• A map is a model: all models are wrong
5. Maps: what they are, what they show
• Map: a representation, by graphical means,
of selected features of the Earth
– A map is a scale drawing of only a selection of
features
• A map is a model: all models are wrong
• If you use an existing map, it may be the
wrong selection of the wrong features at the
wrong scale for your purposes
– If you cannot find a suitable existing map, you will
have to create your own
6. Coates Farm, map of selected features:
simplified detail, shown by line and text symbols
7. Coates Farm, 1:50,000 Ordnance Survey map:
different detail, shown by point, line, area and text symbols
8. Map symbols
colour and texture also used
Manor Farm
Point: towns, buildings, sample points
Line: roads, streams, boundaries, contours
Area (polygon): fields, soils, lakes
Text: names, heights, explanations
9. Map symbols example:
D.R. of the Congo (formerly Zaire)
Town locations:
points
Key to symbols
given in the
“legend”
Lakes & countries:
polygons
Roads and borders:
lines
Colours used to
differentiate
features
Range of text
styles to show
hierarchies.
10. Problems with mapping
The Earth is a spheroid and maps are flat
– map projections
The Earth is huge and maps are tiny
– scale reduction
How do you tell someone which piece of the
Earth your map shows?
– Agreed co-ordinate systems
19. Problems with projections
They always distort one or more of:
– distance
– area
– shape
– direction (angle)
Type of projection chosen dependent on which
of these is most important for the intended
use of the map
20. Scale reduction
Drawing a big World on small paper
Mathematical reduction. 1:1000
– 1 unit on map = 1000 of the same unit on the
ground
21. Scale reduction
Drawing a big World on small paper
Mathematical reduction. 1:1000
– 1 unit on map = 1000 of the same unit on the
ground
Limit to scale reduction set by the thickness of
line that can be drawn
– The red line of an A road on a road atlas is about
300m wide, to “scale”
23. Defining position: co-ordinate systems
How do you say where something is?
– Description: “five miles beyond the hump back
bridge, on the right”
– geographical co-ordinates: Latitude 23o North
Longitude 12o East
– grid reference: 12767m E 1356m N
25. Grid co-ordinates;
applied to a projected map
Base map projected
using a “Universal
transverse mercator”
(UTM) projection.
Grid laid over map.
26. Creating your own map
Basic principles of map creation:
– Forecast the end users’ needs
– Select the features to be shown
– Simplify the features
– Symbolise the features
27. Forecast
• Decide who is going to use your map and
what they will use it for
• Define the geographic extent of their area of
interest
• Find out the level of map use experience of
the end user
• Then start planning your map
30. Compile mapping data and select what you need
Existing
maps
Aerial photos
Farm records
31. The new land use map:
data selected, simplified and symbolised
Mapunit.shp
Agro-forestry
Arable
Built
Campus
Ley
PP
Quarry
W ater
W oodland
Mapunit.shp
Field outlines from
aerial photograph
Land use from farm
records
Field identities
from older map
32. Maps as information sources:
conclusions
• All maps are inaccurate, they are models of
reality
• All maps miss out nearly all possible
information, but should display what you
need
• All maps are out of date, the world is
dynamic and changes
• Despite that, they are an indispensable
tool for conveying information about the
land.