Conceptual models of real world
geographical phenomena
From real world to abstraction
●
Conceptual models
●
Data models and representation
●

Is the geographic world a
jig-saw puzzle of polygons,
or a club-sandwich of data
layers? (Couclelis, 1992)

Maps and GIS are models of reality
They emphasize some aspects of reality in a
cartographic (and database) representation while
ignoring or greatly simplifying other aspects of
reality.
Abstraction
the process of interpreting what can be sensed from
the real world into symbols
Data Modeling
the process of abstraction from the real world for
the purpose of representation in a GIS (or other
information system)

Entities or Fields
Entities
●
space is peopled with 'objects'
–
discontinuous objects, that are spatially delimited by
–
precise edges and, in case, characterized by
specific attributes
recognize the entity then define boundaries and
–
location
“discrete data”
–
administrative boundaries, phonelines,
–
transportation networks

Entities or Fields
Fields
●
space in terms of continuous Cartesian coordinates
–
in two or three dimensions
phenomena that are continuous almost everywhere
–
in their definition domain
attribute vary smoothly and continuously over space
–
understand spatial variation then recognize 'things\"
–
“continuous data”
–
elevation, temperature, satellite data
–

Layers
a logical separation of
●
mapped information
according to theme
each layer is thematic
●
and reflects either a
particular use or a
characteristics
series of overlays
●

Data Models & Representation
Spatial/Geometric
●
location or spatial disribution of a phenomenon
–
Attributes
●
descriptive information associated with geometry
–

Basic Data Models
Vector Data
Model (entities)
Raster Data
Model (fields)

Vector Data Model
The directional linear connection between two
points
The root of vector data model lies in
cartography
Basic elements are points with an x,y
coordinates
Series of points that when joined with straight
lines, form the graphic representation of that
feature unlimited precision

Vector Data Model
A series of points that are connected or joined form a
line. A type of line feature that does not intersect with
any other line is referred to as arcs. A series of arcs
defined a polygon. A series of polygon is a surface
within the vector system.

Object representation
Point (oil wells, fire hydrant)
Lines (railway, roads, rivers)
Area/Polygon (land parcel, forest
stand, lakes)

Topology
Connections & relationships between geographic
features based on location.
Spatial relationships are implicit on map sheets.
Standing on a street corner looking at a map is a
pretty easy way to identify intersecting streets and
properties that are adjacent.
The computer ‘sees’ these relationships by means
of explicitly encoded topology.

Raster Data Models
Establishes a pattern of similar grids or cells over a
geographic area
The location of each cell is defined by its row and
column indices
The value assigned to a cell either reflects the dominant
feature (attribute) at that grid space or indicates the
presence of a preferred feature in case where two or
more features are present within a single grid space
Basic unit in a raster is a cell (or grid or pixel)
Analytically more powerful than the vector based GIS

Raster Data Model

3
5
10
+ 2
4
5
=
10
9
20
Direct calculations using raster layers

Raster or Vector?

Comparison between raster and vector
Raster Vector
Data collection Rapid Slow
Data volume Large Small
Graphic treatment Average Good
Data structure Simple Complex
Geometrical accuracy Low High
Analysis in network Poor Good
Area analysis Good Average
Generalization Simple Complex

Attribute Data

Is the geographic world a
jig-saw puzzle of polygons,
or a club-sandwich of data
layers? (Couclelis, 1992)

References
Burrough, P. A. & McDonnel R.A. 1998. Principles of
Geographical Information System. New York, USA:
Oxford University Press
Neteler, M. & Mitasova, H. 2004. Open source GIS: a
GRASS GIS approach, 2nd edition. The Netherlands:
Kluwer Academic Publishers
Heywood, I. et. al. 1998. An Introduction to Geographical
Information System. New York, USA: Addison Wesley
Longman

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