eg1106 geographic information: a primer mark cresswell: room e449b 15th october 2004 maps &...
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EG1106Geographic Information: a primer
Mark Cresswell: Room E449b
15th October 2004
Maps & Representation
What is a map?How do maps provide information?Map Abstraction and GeneralisationUsing maps to communicateGIS
Practical Today and IN TWO WEEKS
TOPICS
Maps convey information about a place by graphical (or tactile) means
Use of lines, points, symbols, shading and contours convey essential elements about a place.
Every map has a spatial frame of reference - such as gridlines (Ordnance Survey for example), geographical co-ordinates (latitude & longitude) or more localised (postcode or political wards)
Maps rely on a simplification of reality
What is a map?
Is this a map?
What is a map?
North America
Central America
South America
Western and Central
Europe
Africa
Eastern Europe
Asia
Australia and New Zealand
Is this a map?
What is a map?
Do all maps have to faithfully replicate even gross features of reality - or can they be exploited to communicate concepts?
What is a map?
The map of the London Underground was originally drawn in the 1920s by Beck who was an electronics draughtsman
The Tube map is easily understood by everyone who uses it - but it bears little relation to the “real” railway network layout.
How do maps provide information?
Scale and Representation
All conventional maps have a SCALE - this tells the user how the features on the map relate spatially to the world it depicts.
Without a scale, maps do not inform the user of key information such as DISTANCE and SIZE.
All maps show a simplification of reality
Complex real-world features are deconstructed and projected onto a 2-dimensional spatial reference system
Major features become a collection of lines, points, polygons and symbols
Cartographers will take an aerial photograph and produce a map retaining the essential elements - but without the complexity and unimportant information
Map Abstraction and Generalisation
GENERALISATION - varies the quantity of detail according to the scale.A map at a scale of 1:100 000 will have only a quarter of the space available for portraying information about a region than a map at a scale of 1:25 000
Map Abstraction and Generalisation
ABSTRACTION - This is the process whereby complex features such as drainage channels, road networks and buildings are reduced to:
Linesthe thickness of which may not be related to reality
Symbolsa church or hospital will have a standard symbol regardless of the size of the hospital or religious denomination of the church
Map Abstraction and Generalisation
A map does not have to be a road atlas or A to Z format of publication
Maps can be used to display any data that has a spatial (geographic) component.
We can show a map of a region or country and graphically show data in the form of colours and/or symbol size. These are CHLOROPLETH maps.
Using Maps to Communicate
Using Maps to Communicate
Ocean
Projected population in 20000.2 M - 16.4 M16.4 M - 48.5 M48.5 M - 107.5 M107.5 M - 270.1 M270.1 M - 1304.5 MNo Data
6000 0 6000 12000 Miles
N
EW
S
World
Using Maps to Communicate
Ocean
Life Expectancy39.8 - 49.549.5 - 5959 - 67.567.5 - 7373 - 79.3No Data
6000 0 6000 12000 Miles
N
EW
S
World
GIS
Geographical Information System
Based around computer software
Maps become DYNAMIC – they can be updated as often as the information changes
Maps can be carried on digital devices – handheld computers with high resolution screens – updateable in real-time.