For our first Geospatial Frequently Asked Question (G-FAQ) of the New Year, I focus on a topic that is extremely relevant with the launch of our new Marcellus-Utica lease hold layer. Many times in the past few weeks, I have been asked to put together a map of our leasing layer but upon delving deeper into the client’s specific needs, it becomes apparent that what they are really asking for is a spatial analysis that is predicated upon the mapping data we can provide. It is my feeling that free mapping software such as Google Earth and Microsoft Virtual Earth has blurred the line between a map and spatial analysis by giving users tools to measure distances, zoom in and out, turn layers on and off and more.
So for this G-FAQ I explore the line between a map and a spatial analysis, specifically trying to address this set of core questions:
What is a map? What is spatial analysis? What purpose does each serve? How is a map (or perhaps we should call it mapping data as you will see below) used to complete spatial analysis? Is there a way for me to complete my own spatial analysis with free tools?
In order to answer this set of questions, we need to start off with a definition of a map. While many definitions I have seen tend to include a degree of social context or spatial interpretation, I whole heartedly disagree with this definition and believe these authors to be conflating a map with spatial analysis – a topic I address in more detail below. Instead, I tend to follow a much simpler interpretation of a map put forth by a leading cartographer at the University of California, Los Angeles, Dr. Norman Thrower:
A representation, usually on a plane surface, of all or part of the earth or some other body showing a group of features in terms of their relative size and position.
So then a map is simply a picture, a poster or even a trail map printed on the back of a microfiber cloth. A map is meant for human beings to extract important information about their surroundings and often to estimate the impact of these spatial patterns on their own existence. But this interpretation is not part of the map itself. A map is merely a means to an end; or a tool for use in spatial analysis.
The next set of questions we must address center on the definition of spatial analysis. In the academic world, and even on Wikipedia, there are many formal definitions of spatial analysis that conflate it with a set of statistical and other mathematical techniques such as spatial regression and interpolation. While I certainly recognize these studies as core components of spatial analysis, they are certainly not the only techniques we employ when we analyze data. I chose to define a spatial analysis as:
Any interpretation of geographic information to answer a set of questions we might have about our surroundings.
With an all encompassing definition such as I have put forth, we capture all forms of geographic questions one might have and can answer with map data. For example, what if you wanted to know all of the schools in a county that are within 1,500 feet of a police station-fire department and a hospital. While this ‘spatial analysis’ is not the complex sort of analysis many geographers and users of ArcGIS (which is the most widely used software package to analyze spatial data) would pride themselves on, it is most definitely a question that can only be answered by:
- Gathering and preparing a set of mapping layers that shows the locations of the county limits, schools, police stations and fire departments.
- Combining them together in a geospatial software application that lets you view and analyze the layers all at once.
- And then finally running the required set of spatial filters and queries to reach the answers you seek.
From the explanation above, it should be apparent that a map or mapping layers alone do not complete a spatial analysis, rather they are the inputs required to get the answers you seek. As a quick side note, I introduced the term ‘mapping layers’ above and now define this to be any dataset with an associated coordinate (e.g. latitude and longitude), such as the locations of the police departments, fire stations and schools in a county. ‘Mapping layers’ are the raw data used to create a finished ‘pretty’ map and/or are used in conjunction to complete a spatial analysis.
Now let’s turn our attention to a visual representation of spatial analysis. In the screen captures below are the major steps involved with the spatial analysis outlined above – along with a map showing the results of this analysis. While tools like Google Earth are effective for answering many geospatial questions, most lack crucial features with which users can sort, filter and build upon spatial data to answer more complex queries. For the spatial analysis below, I utilized Esri’s ArcMap 10.0 along with free Geographic Information Systems (GIS) mapping layers that accompany ArcMap.
In the screen capture for Step 1 of this analysis, I brought mapping layers for the County of Boulder, Colorado (including the locations of schools, police departments, fire stations and hospitals) into ArcMap and then displayed them in a fashion that made visual and spatial queries possible. For this article, I will focus on a small subset of these mapping layers centered in North Boulder within our city limits.
In Step 2 of the analysis, I used the BUFFER tool in ArcMap to calculate a 1,500-foot radius circle around each point that defines the center of a hospital in Boulder County. These 1,500-foot circles are displayed on the screen capture below in blue.
In Step 3 of the analysis, I used the same BUFFER tool to calculate a 1,500-foot circle around each of the police and fire buildings in Boulder County. By turning this layer yellow and making it 50% transparent, when it is overlayed on a blue background (i.e. a circle that defines a 1,500-foot circle around a hospital) the result is a green area where the two circles overlap. The green polygons define both of the initial search criteria for this spatial analysis which was to locate the schools that were within 1,500-feet of both a hospital and a police station and/or fire department. In this subsection of Boulder, Casey Middle School is the only school which meets both of these criteria.
Hopefully this relatively simple ‘spatial analysis’ and accompanying ‘map’ illustrates three important points about the relationship between these geographic terms:
While there are many tools you can use for spatial analysis and making maps, many of them are quite costly. One very powerful free option is Quantum GIS – you can find out more about this freeware GIS option here. In the next edition of G-FAQ, I will pick up on this conversation by examining the components and features of an effective map.
- For many people, a spatial analysis is what they seek when they might be requesting a map. In that, they have a question they want answered where mapping data will help to answer it but is not sufficient without subsequent analysis.
- Any good spatial analysis should have an accompanying map that can help to illustrate some/all of the answers to your questions.
- A spatial analysis can be much less complex than the name may lead you to believe!
Do you have an idea for a future G-FAQ? If so, let me know by email at email@example.com.
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Brock Adam McCarty