Map 1: What is a GIS map? A GIS map contains points, lines and polygons
What is a GIS map? Its a digital map that has two important features…
- Coordinate system: A GIS map is a computerized map that’s in a coordinate system. The coordinate system allows it to be related to other GIS maps that are in the same coordinate system (ie. you could buy a map of cafe’s on the internet and so long as it was in the same coordinate system as your map, the two maps would overlay each other in a GIS). This is in contrast to a computer graphics map, the features in which can only be related to other features in the same map.
- Database: Each feature in a GIS map has a database entry describing it. This means that information about a map feature can be stored, and custom maps produced based on the information in the database. Consider for example, a power pole. It might be made of wood, would have been installed on a particular date and will carry wiring rated to carry a certain voltage. By using a database query techniques, a GIS professional could produce a map of “all high voltage wooden power poles installed during the winter months”.
These two features of GIS maps mean that maps from many different sources can be related to each other, compared and analyzed, rather than just “looked at”.
A GIS map has three deceptively simple categories of map features that are described in table 1 below – points, lines and polygons (areas).
Table 1 – What is a GIS map?: It may seem an overkill to have a map like Map 1 as a GIS map because you can easily see all the important features on it (ie. roads, parks and schools). However, imagine how useful this GIS map would be if you needed to answer a question such as “how many schools are there in an entire country”!
|Points||You can see a school the map||You can find out how many schools are on the map?|
|Lines||You can see roads and streets||You can find out the length of all roads on the map?|
|Polygons (Areas)||You can see a park||You can find out how big the parks are?|