Integrating ArcGIS and Google Earth for Crime Analysis
I’m going to be taking a slightly different approach in this post than I have in previous posts. Typically, GeoChalkboard focuses on providing how-to information regarding the use of ESRI, Google Earth/Maps, and other geospatial technologies. As such we normally provide very detailed instructions regarding how to use certain aspects of these software technologies. However, in this post I’m going to describe at a higher-level the output of a crime analysis project I recently completed for Texas State University. My intent is to expose you to some of the possibilities for integrating these technologies in a way that takes advantage of the advanced analysis and visualization techniques that are possible. Based on some of my previous posts you can probably tell that I’m particularly interested in the integration of ArcGIS Desktop with Google Earth. In my opinion, this is a great combination for analyzing and presenting spatial data. ArcGIS at the desktop level is a fantastic tool for analyzing and modeling spatial data, and Google Earth provides a visualization platform that is second to none. By combining these two products you can provide not only advanced analysis techniques, but also present compelling visualizations of the resulting data.
Dr. Tina Cade in the Horticulture Department at Texas State University approached GeoSpatial Training Services regarding the use of geospatial technology for determining the effect of community gardens on crime rates in the areas surrounding these small plots of land that are gardened by a group of people. Community gardens have many benefits to both the human and natural environment including neighborhood beautification, social interaction, and as a catalyst for neighborhood development. Get more information on community gardens here. This particular project was interested in the effect that these community gardens would have on crime rates in the surrounding areas in the Houston, Texas urban area.
The application of geospatial technology to this project had both analysis and visualization components. A number of statistical techniques were used to measure the effectiveness of community gardens in deterring crime, and ArcGIS was used to create various datasets that were used in the statistical analysis. However, I’m not going to focus on these aspects of the project in this post, but will instead focus on the techniques employed in the visualization component of the project. These techniques, carried out by using a combination of ArcGIS, Spatial Analyst, Arc2Earth, and Google Earth provided a strong combination of tools to generate and visualize crime data in Houston, and can be used as a general platform for many projects across a wide variety of industries. For visualization purposes, the study called for the creation of raster based crime “heat-maps” based on ¼ mile cell size along with 3D views of the same data.
The primary sources of data for this study were address level crimes for the year 2005 as provided by the Houston Police Department and the addresses of all community gardens in the Houston area. Crime data at the address level had already been geocoded into a shapefile format. Community garden data was also geocoded to a street level. We were primarily interested in the neighborhood level effect that community gardens would have on crime rates so the study areas for each community garden were relatively small (1/4 mile and 2 mile radii).
Creating the Heat-Maps
For visualization purposes, the study called for the creation of various heat-maps that would enhance the visualization of crime data in Houston. To accomplish this we used a combination of ArcInfo with the Spatial Analyst Extension, Arc2Earth, and Google Earth. Using our geocoded crime data, a series of raster grids were created by crime type using Spatial Analyst using a ¼ mile grid size. We then symbolized the resulting grid surface in ArcGIS and exported as an image overlay using Arc2Earth. Arc2Earth is an ArcGIS extension that can be used to export your GIS format data into a KML file for visualization by Google Earth. Here are some examples of the resulting Google Earth format crime heat-maps. This particular map shows burglary hot spots for the City of Houston in relation to community garden locations surrounded by a 2 mile radius (circles).
Creating 3D Maps
In addition to the heat-maps we also wanted to be able to visualize the data in 3D. To accomplish this we used ArcGIS to drape a vector fish-net composed of ¼ mile grids on the City of Houston. Next, we used a spatial join in ArcGIS to count the number of crimes by type in each grid. We used the resulting field as an elevation value in Arc2Earth to export the 3D screenshots that you see below.
For more information on integrating ArcGIS and Google Earth please consider our “Integrating ArcGIS Desktop and Google Earth” virtual training course.