Answering Questions with GIS

GIS is fundamentally used to answer questions and make decisions. To use GIS properly, it is important to know what you want to ask and follow a disciplined process for getting the answer.

1. Frame the question.

Start your GIS analysis by figuring out what information you need. This is most often in the form of a question:

• Where were most of the burglaries last month?
• How much forest is in each watershed?
• Which parcels are within 500 feet of this liquor store?

Be as specific as possible about the question you want to answer. This will help you decide how to approach the analysis, which method to use, and how to present the results.

This map was used to answer the question "Where is the best place to land a Mars Exploration Rover?" Learn more.

2. Select your data.

The type of data and features you work with help determine the method you use. Or, if you know you need to use a specific method to answer your question, you may find you need additional data.

Data can come from any number of sources—databases within your organization, contact managers, CAD files, the Internet, commercial data providers, government organizations, and so on.

The data you choose and where you get it depends on your needs and budget. Most critical is that the data be good quality, accurate data.

This water utility map shows five sets of data: parcels, building footprints, grid lines, streets, and pipes color coded by replacement status. Only the data necessary for understanding pipe locations and status was displayed. Learn more.

Learn more about data types, data models, and sources of data.

3. Choose an analysis method.

Decide which analysis method to use based on your original question and how the results of the analysis will be used.

For example, if you are doing a quick study of burglaries in a city to look for patterns, you might just map the individual crimes and look at the maps. If the information will be used as evidence in a trial, however, you might want a more precise measure of the locations and numbers of assaults for a given time period.

This seismicity map shows the time dependent relation between the inception of geothermal power production and the occurrence of earthquake activity from 1967 through 1995 in Santa Rosa, Califorina. This study used temporal analysis as the analysis method of choice. Learn more about the study.

4. Process the data.

Once you've selected the analysis method, you'll need to process your data in a way that makes sense for your goal.

If you are mapping where things are located, you may need to assign geographic coordinates, such as latitude and longitude or address, to your data and assign category values to the data.

If you are mapping quantities, such as number of vegetation types in a state park, you may need to choose a classification scheme and decide on how many classes to represent your data.

If you are trying to find out what is inside, you may need to measure an area or combine different layers of information.

5. Look at the results.

The final step is to look at the results of your analysis and take action based on those results.

Your results can be displayed as a digital map, printed as a paper map, combined with spreadsheet-like tables or charts, or displayed as such. Though a lot of emphasis in GIS is in making maps, the software is flexible enough to allow you to display your results in the format that best suits your needs.

This map was created to locate explosive remnants of war in Iraq to help in planning the cleanup effort. Learn more.