Lets define GIS

There are many ways to define GIS …and by GIS I mean a Geographical Information System. GIS combines spatial data (maps), temporal data (when things on a map happen) and attribute data (what things are). It uses these to create maps that summarize information in ways that make it incredibly easy to communicate ideas and facts.

GIS is an incredibly useful information tool for professions as diverse as marketers, environmentalists, health researchers and social researchers.

In this post I want to talk a little about paper maps and then illustrate what a GIS can do by using a couple of examples.

The Problem with Paper Maps

Although paper maps still have their place, they are fast becoming redundant.

They rarely fold up properly, they often contain inaccurate or out-of-date information, and can have so many creases that its nearly impossible to make out road names and directions.

We’ve all used paper maps and wished they were better suited to our needs. If only you could add your own information to the map and have it reflect those changes instantaneously.

The technology to create your own custom maps is here, and, to be honest, has been for some time now.

The software is called Geographic Information Systems (GIS ). Following are two examples of GIS applications.

Two Examples Of GIS Applications

GIS Application #1 – Site selection for crops

Define GIS with an example: Typical maps used to create a crop suitability map
Figure 1: Typical map layers that are used in a Crop Suitability map.

Imagine that you’re looking for the perfect place to grow a crop. You know the crop’s optimal growing conditions in terms of elevation, aspect, rainfall, temperature, soil type and existing vegetation cover.  You could match these growing conditions to GIS maps of them to find suitable farmland. Simplistically, its a 5 step process…

Step #1: On a piece of paper, write down the optimal growing conditions for your crop. These will include conditions relating to things such as elevation, aspect, rainfall, temperature, soil type and existing vegetation cover.

Step #2: Create GIS maps of each of the growing conditions that you documented and then then in the GIS change each map to be a crop suitability map.

For example, a rainfall map might be changed to have the following three crop suitability classes…

  • High rainfall = Highly suitable,
  • Moderate rainfall = Moderately suitable
  • Low rainfall = Unsuitable

Step #3: Create a GIS map of “constrained” land

You will need to exclude some places up-front on the basis of things that are a limitation for the crop – for example, slopes that are too steep to safely drive a tractor, or soils that are too boggy for your crop to grow.

Step #4: : Combine the Crop Suitability maps into a single map representing overall land suitability for the crop.

At the heart of all the techniques for doing this is a technique known as map overlay. That simply involves overlaying all the map themes onto each other…the most suitable areas in the resulting maps are those that are covered by the greatest number of “Highly Suitable” areas.

Step #5: Overlay the map of Constraints.

Then you overlay the map of constraints onto the Crop Suitability map to produce a map of suitable sites.

If you’ve read my other posts that talk about the accuracy of GIS maps you will know that such a map is unlikely to be completely accurate, but rather an excellent starting point for putting on your boots and doing some fieldwork.

GIS Application #2 – Site selection for a new Delicatessen.

Define GIS with an example: Density of Greek People KM2
Figure 2: The density of Greek people in census areas local to me, and overlaid with local delicatessens.

Imagine you were planning to open a delicatessen.  The number one rule of marketing is to sell only goods that people want to buy. With this in mind, there are three simple steps that for informing where you would locate your delicatessen…

Step #1: Create a map showing existing delicatessens and the ethnic groups they service. Each delicatessen could be shaded a different colour depending on the ethnic group it serviced. The example in figure 2 only shows Greek delicatessens.

Step #2: Create a series of census maps showing where various ethnic groups are concentrated in your region. Census maps showing the density of various ethnic groups per square kilometre are easy to produce in a GIS. Figure 2 is a map showing the density of Greek people in census areas local to me.

Step #3 – Overlay the maps: Overlay the population density map with the delicatessens map with in your GIS. This would allow you to see in which areas each ethnic group is under-serviced by delicatessens selling the style of foods they like to purchase. Figure 2 is a map showing the population density of Greek people and is overlaid with another map showing existing delicatessens.

Lets define GIS…well I’ve made a start. However GIS applications are not limited to site selection for crops or delicatessens. You can use this technology for thousands of applications that are only limited by imagination.

Be Sure to Get Your Free GIS eBook. In it there are many GIS applications that will help you further along the path to define GIS. Click Here and take your education to the next level.

Figure 1 source:

Adapted from…Nikos Krigas, Kimon Papadimitriou and Antonios D. Mazaris, GIS and ex situ Plant Conservation, Chapter 9 in “Application of Geographic Information Systems”, book edited by Bhuiyan Monwar Alam, ISBN 978-953-51-0824-5, Published: October 31, 2012