School of Environmental Sciences University of East Anglia GIS: An Introduction Andrew Lovett School of Environmental Sciences University of East Anglia a.lovett@uea.ac.uk

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

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.

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

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.

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.

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.

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.

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)

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.

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

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.