1. School of Environmental Sciences University of East Anglia
GIS: An Introduction
Andrew Lovett
School of Environmental Sciences University of East Anglia

2. What is a GIS?
A Geographical Information System (GIS) can be defined in several different ways.
One common approach is to emphasize the functions performed e.g.
“ a system for capturing, storing, checking, integrating, manipulating, analysing and displaying data which are spatially referenced to the earth”
Report of the Chorley Committee to the UK Department of the Environment, 1987.
Chorley Report – 1st official UK report re GIS / Landmark development GIS in UK / Chorley was the president/chairman of Royal Geographical Society (RGS)
Spatially Referenced – i.e. indicate position of feature on Earth’s surface – ask for examples

3. Layers of Information
A GIS can display and work with many different sets of information at a time (e.g. population, elevation, satellite imagery) – these are usually called layers or themes.
You could imagine these as transparent maps overlaid on each other – the GIS allows you to see how layers relate, and to make decisions based on multiple data sets.
The spatial reference provides a means of data integration.

4. What is a GIS? A key influence on the success of a GIS project
GIS Data
Description and
Representation
Operational GIS
Analysis and
Presentation
Feature
Polygon
Line
Building
Street
Water
Line
Pump House
House
Users
Interpretation and
Decisions
Real World
Source: Longley et al. (2005) p. 178

5. Types of GIS Data
Just as maps do, representing real world features in a GIS database also invariably involves some simplification and abstraction.
There are two broad types of information:
Continuous data can be measured anywhere (e.g. elevation, temperature) and forms a surface.
Discrete data show individual objects and where they are located, as point, line or area features.

6. Discrete representation of UEA Broad. OS Land-Line map data.
Types of GIS Data
Some types of real world features can be described using either approach e.g. a lake.
Continuous representation of UEA Broad. Band 4 reflectance on Landsat TM.
Discrete representation of UEA Broad. OS Land-Line map data.
Factors such as spatial scale and the intended use of the data can also influence the approach to conceptualisation.

7. Types of GIS Data
Continuous and discrete data lend themselves to storage and use in different ways, leading to two common data formats:
Raster format is effectively a grid of information representing a single variable or category, at a defined resolution. It lends itself well to continuous data.
Vector format shows data as made up of point, line and area entities, but boundaries and locations are not confined to a grid. It lends itself to discrete data.

8. Raster Data A B C
The original map (A) is divided into a regular grid of cells (B).
Each cell is assigned a number (C) representing the feature present. All cells have values so the structure is space filling.
Adjoining cells may also have different values e.g. for elevation.

9. The accuracy with which shapes are shown depends on the cell resolution (the length of one side of a cell).
Rasterised at 5m resolution
(higher resolution)
Rasterised at 10m resolution
(lower resolution)

10. Vector Data
Feature ID for polygon
discrete points, lines or areas (polygons) are used to represent features the locations of which are defined by sets of x,y coordinates
different from raster in that attribute information is stored separately from spatial data
Features are represented as sets of points, lines and polygons (areas). In vector datasets, attribute information is stored separately from spatial data and joined (i.e. linked) through unique feature IDs.

11. Questions a GIS can Answer
Source: Kraak & Ormeling (2003) Cartography: Visualisation of Geospatial Data, 2nd Edition, Prentice Hall, Harlow,p.7.

12. The Development of GIS
Personal Digital Assistant (PDA)
Internet GIS, Geobrowsers
1960s-1980s
1990s
2000s
The global market for geospatial products and services was estimated at $30 billion per annum in 2005.