The Map as a Model of Geographic Data

The Language of Spatial Thinking

Doç.Dr. Necla ULUĞTEKİN

İTÜ

Spatial thinking requires us to be able to

select observe measure catalogue

characterise what we encounter.

Data are collected

•in the field basic (absolute) data•remote sensing basic (absolute) data•existing maps derived data•catalogues derived data• ...

A knowledge about cartographic methods will increase a portion of our spatial vocabulary

that we have called graphicacy.

• Existing maps into the GIS

– Different level of generalisation

– Different level of scales

– Different projections

– Different symbolisation

Cartography is the art, science and technology of making maps

together with their study as scientific documents

and works of art. (1973, ICA)

Cartography is the organisation, presentation, communication and utilisation of geo-information in graphic, digital or tactile form.

(ICA, 1991)

Map

• an abstraction of reality, it is not reality itself.

• the fundamental language of geography.

• symbolise image of geographical reality– representing selected feature– representing feature relationships– representing characteristics

Maps can be used

• Navigation

• Exploration

• Discovery

• Interactive computer navigation

• Education

• Forecasting

• …

Primary Types of Maps

• Topographic Map (General Reference)

• Thematic Map

GIS works together

• geology

• surveying

• soil science

• other disciplines

GIS is used in these disciplines,in addition to

• Geological maps

• Topographic maps

• Cadastral Maps

• Soil Maps

The thematic context of GIS includes

• Vegetation maps

• Transportation maps

• Animal distribution maps

• Utility maps

• Urban plans

• Zoning maps

• ...

GIS is

• hardware

• software

• people (organisation)

• data

GIS is about

• data integration

• spatial analysis

• link with application based models

The traditional approach to mapping called the

communication paradigmThe map was a final product designed to communicate a spatial pattern through the use of symbols, class limit selection and so on.

The traditional method was limited because raw, pre-classified data are not readily available to the map user

Communication Paradigm

Real World CartographerConception

Map

Map UserConceptions

The alternative approach to cartography which is computer technology called

the analytical or holistic paradigm

Maintains the raw attribute data inside a computer storage device and display data based on user needs and

user classifications

Map Scale

• Scale is the ratio of distance on the map to the same distance as appears on the earth

• Methods of illustrating map scale– verbal scale 1mm = 1000 mm– representation fraction 1:1000– graphic or bar scale

• 1:1000 1:5000 1:10 000 1:25 000

Generalisation

• Every map is, in principle, generalised.

• Why?– increasing density of the map contents due to

scale reduction– limit of sharpness of the eye, printing capabilities– minimum sizes

• the choice of degree of generalisation depends on aim and scale of the map.

Map Characteristics

• Maps as images of the world, represent the locations of objects, as well as their qualities or magnitudes.

• Objects are represented as points, line, areas or surfaces in the computer memory as like in the reality.

Objects

Entities Attributes GeometricData

house owner coordinates

parcel use coordinates

Levels of data measurements

• qualitative or nominal level

• ordered or ordinal level

• quantitative or interval level

GRID SYSTEMS for MAPPING

•Geographical Coordinates based on latitude and longitude for the locating of objects or features on the spherical earth or its reference globe.

•Rectangular Coordinates or Plane Coordinates allows us to locate objects correctly on these flat maps.

Map Projection• The three-dimensional geographic relationships

of the Earth surface must be transformed to the two-dimensional plane of the map by any of several procedures called map projections.

• Division of map projections according to their properties– conform projections– equivalent (Equal-Area) projections– equidistant projection – others

Division of map projections according to their construction

• cylindrical projections

• conic projections

• azimuthal projectionsDivision of map projections according to their

aspect• Polar (regular)• Equatorial (transversal)• oblique

UNIVERSAL TRANSVERSE MERCATOR PROJECTION (UTM)

• cylindrical, equatorial, conform projection• the area is covered by 80° South - 84° North latitude• the earth is divided into 60 zones (each 6° longitude)• 180° West Longitude - 0° - 180° East Longitude• 20 latitudinal belts (each 8° latitude)• scale factor = 0.9996• origin shifted 500 000 m to east (false easting)• origin shifted 10 000 000 m to south for the southern

hemisphere

Projection surfaces

The Cartographic Process

• data collection (first step of GIS)

• data compilation (classification and symbolism)

• map production

• map reproduction (output of GIS)

Map symbolism

• According to their dimensional characteristics – point symbol (location and identity)– line symbol (linear characteristics)– area symbol (provinces, countries, soil units)

Map symbolism

• According to their shape cartographic symbol grouped in three main categories– pictorial or descriptive symbols– geometric or abstract symbols– letter or number symbols– other symbols (pie graph, bar graph etc.)

Thematic Maps

• dot map is a proportional changing in data

• choropleth map (value-by-area mapping)

• statistical mapping – class interval selection

• equal class or constant interval methods• variable intervals - arithmetic, logarithmic, other

mathematical series, unsystematic … (contour line on a topographic map class interval selection for choropleth maps.)

The Nature of Spatial Data

• model construction and geographic object selection (surveying, photogrammetry, remote sensing, recycling old maps, statistical

surveys)• select and construct cartographic representation (road

map, topographic map, ...)• medium output (paper map or on-screen map)

• Reality digital landscape model digital cartographic model map mental map

What we learnt

• new perspective (map, scale, communication, ...)• new concepts (cartography, generalisation,

projection, ...)• new people