21 November 2011
(Step 5 of 7 of eSpatial’s “Get started using GIS in 7 easy steps” series.)
- In Step 1, you created a prioritised list of questions you wanted to answer.
- In Step 2, you identified the data you needed to answer those questions.
- In Step 3, you gathered and formatted data.
- In Step 4, you created a map and uploaded your data.
Now you’ll really begin to see the value of using GIS to analyse your data. Your next step is to create queries that match the list of questions that you drafted in Step 1.
We’ll begin by covering some basics about queries.
What is a query, and why is it important?
A query is a specific question that enables GIS software to display your data.
The results of your query may be a subset of your data, or all your data, sorted by a particular attribute.
For example:
- Jane wants to plan ahead to see how many fire hydrants need to be serviced next month. She creates a query to see all fire hydrants with a “service due” date for next month. Her query returns only the fire hydrants that are due for service next month.
- Mary wants to see the average spend per month for customers in a specific area. She creates a query to see the average monthly spend of customers in a particular zip code. Her query returns only the customers who live in that zip code, and their average monthly spend.
How are the results of queries returned?
In GIS software, each query is returned as a layer of data that is displayed on your map. So if you have 3 queries, you have 3 layers of data that you can view – together or separately – on your map.
If you have a broad question, you’ll get the most value out of creating multiple, broad queries and viewing all the layers of results individually and together.
If you have a very specific question, it’s best to create a more complex query that will give you the specific results you’re looking for.
Successfully creating a query
It’s important to understand that you can create either a simple of a complex query – how complex your query is really depends on how complicated your question is.
Get your prioritised set of questions – and the list of data required to answer the questions. Take your first question and data requirements, and break it down into a sub-set of questions.
For example, if your question is: “What’s the average age, and most common gender, in areas around our Chicago retail stores?”, you’ll need to create the following queries:
- All your retail store locations in Chicago.
- Average age demographics (in the surrounding areas, if you can be specific).
- Gender demographics (in the surrounding areas, if you can be specific).
Each vendor’s GIS software handles queries a little differently – so we can’t tell you what to do step by step, but it shouldn’t be too difficult once you have your list of questions at hand. If you’re not sure what to do, check out the software’s Help files.
Finished creating queries? You’re ready for Step 6: Style the output.
