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.