Village of Wellington GIS

How GIS Works

A GIS stores information about the world as a collection of thematic layers that can be linked together by geography. This simple but extremely powerful and versatile concept has proven to be invaluable for solving many problems from tracking delivery vehicles, to recording details of planning applications, to modeling how a brush fire will move across a landscape.

Geographic information contains either an explicit geographic reference such as a latitude and longitude or national grid coordinate, or an implicit reference such as an address, postal code, census tract name, forest stand identifier, or road name. Implicit references can be derived from explicit references using an automated process called "geocoding." These geographic references allow you to locate features (like a business or forest stand) and events (like a chemical spill) on the surface of the earth for analysis.

Geographic information systems work with two fundamentally different types of geographic information--the "raster model" and the "vector model."

In the vector model, information about points, lines, and polygons is encoded and stored as a collection of x,y coordinates. The location of a point feature, such as a bore hole, can be described by a single x,y coordinate. Linear features, such as roads and rivers, can be stored as a collection of point coordinates. Polygonal features, such as sales territories and river catchments, can be stored as a closed loop of coordinates. The vector model is extremely useful for describing discrete features, but less useful for describing continuously varying features such as soil type or surface elevation data.

The raster model evolved to model such continuous features. A raster image comprises a collection of grid cells rather like a scanned map or picture. Every cell can have a unique value. Both the vector and raster models for storing geographic data have unique advantages and disadvantages and modern GISs are able to use both in concert to effectively perform the most complex analysis tasks.