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Maps and mapping
Spatial models of the real World:
Traditional paper maps
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
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
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
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
Coates Farm, map of selected features: simplified detail, shown by line and text symbols
Coates Farm, 1:50,000 Ordnance Survey map: different detail, shown by point, line, area and text symbols
Map symbolscolour 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
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.
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
Map projections: flattening out the curved Earth
Map projections: flattening out the curved Earth
Map projections: flattening out the curved Earth
Three mathematical projection examples
Three mathematical projection examples
Three mathematical projection examples
Three different projections same place
An interrupted projection: distortions concentrated into “unimportant areas”
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
Scale reductionDrawing a big World on small paper
Mathematical reduction. 1:1000– 1 unit on map = 1000 of the same unit on the
ground
Scale reductionDrawing 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”
Same place, different map scale
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
Geographical co-ordinatesLatitude and longitude
Grid co-ordinates; applied to a projected map
Base map projected using a “Universal transverse mercator” (UTM) projection. Grid laid over map.
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
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
Compile mapping data and select what you need
Existing maps
Compile mapping data and select what you need
Existing maps
Aerial photos
Compile mapping data and select what you need
Existing maps
Aerial photosFarm records
The new land use map:data selected, simplified and symbolised
Mapunit.shp
Agro-forestry
Arable
Built
Campus
Ley
PP
Quarry
Water
Woodland
Mapunit.shp
Field outlines from aerial photograph
Land use from farm records
Field identities from older map
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.