Within a GIS data is displayed on one of three formats: points, lines or polygons. How that data is represented depends on the attribute data which is linked to the spatial elements. For example, points could represent cities. If we only have the names of the cities we would class this data as nominal as we only have the names. If we have non numerical data which also describes the size of the city then this could be shown as an interval class where data is represent by for example, small, medium and large depending on population size. Information about the population size of the cities which would enable us to additionally represent the points as numeric values would be termed an ordinal data class.
This ordinal data could then be shown at different point sizes depending on the population of each city. Finally we could class the data as a ratio class based on the numeric value of each city's population. Each point would then be sized within a designated ratio band according to the numeric value of the population.
Depending on whether we have access to relevant nominal and numerical data will define how we can create maps which provide us with solutions to the problems we are presented with. If we only have limited information we will only be able to make limited decisions from what our maps represent. Sometimes we can enhance data by combining the map's attribute data with other information to achieve successful analysis. For instance, if we have a map of city points there may also be another data table which contains population or other relevant data which could be linked to the map. As long as we have a relevant field in the attached data, which enables a successful link to occur, such an approach is feasible.
If you would like to further explore how GIS could help your organisation jps services offers one and two day training courses in QGIS, ArcGIS and MapInfo.
Joe Short BSc has been involved with various mapping solutions since 1993. If you are considering implementing a GIS or have ArcGIS, MapInfo or Quantum GIS training requirements I would be happy to be of assistance to your organisation.