Table of Contents
- Exploring Patterns of Crime In Los Angeles County Using A Density Surface Model
- Setting up Your Workspace
- Preparing the Data
- Skill Drill: Clipping the LA City Boundaries to the Census LA County Boundary
- Skill Drill: Adding XY Data
- Skill Drill: Clipping the Crime Data to the Census LA County Boundary
- Skill Drill: Creating a Subset of the Data Based on Crime Category
- Changing Global Environment Settings for Raster Processing
- Creating a Density Surface Model Using the Simple Method
- Creating a Density Surface Model Using the Kernel Method
- Skill Drill: Creating A Density Surface Model Based on Your Criteria
Skill Drill: Adding XY Data
Navigate to the Los Angeles County GIS Data Portal and use the keyword crime to search for recent crime data from the LA County Sheriff’s Department.
There are several datasets available for download. For this scenario, you will be using the Part 1 and Part 2 crimes from the last 30 days located under the heading, Part I & II Crimes. Download the comma separated values (CSV) file to your original folder.
If for some reason the data is not available, please notify your instructor.
Launch Microsoft Excel open the Part_I_AND_II CRIMES.csv file. Here you will see a table of crimes recorded by the Los Angeles Sheriff’s Department over the past thirty days. Take a moment to read through available information about the crimes. Included in the table are a series of fields you will use in your density surface model. Each crime record has a crime category and code. Most of the records also contain a set of State Plane Coordinates (SPC). With this dataset, you can explore a wide range of crime patterns in Los Angeles County. After you have looked over the CSV table, be sure to close Microsoft Excel before returning to the ArcGIS software.
Because the records are geocoded, you will be able to add them to ArcMap as XY data. Unlike most XY data, the coordinates in this CSV table are not currently in the geographic spatial reference system WGS 1984. The County of Los Angeles maintains its GIS data using the State Plane Coordinate System (SPC). The XY values in this CSV table are in NAD 83 StatePlane California V FIPS 0405 (US Feet). When adding XY data, the ArcGIS software is unaware to which spatial reference system these values belong. ArcMap will assume, incorrectly, that the spatial reference is the same as the dataframe. You must indicate in the Add XY data dialog box that this series of XY values belong to the NAD 83 StatePlane California V FIPS 0405 (US Feet) spatial reference system. If you do not, your crime data will likely end up somewhere in the ocean.
After adding XY data, the ArcGIS software will create a temporary events layer. In many ways, the events layer appears to be similar to a shapefile. However, it is only a temporary representation and does not have an associated database.
Export the events layer as a shapefile and save it to your working folder. You should now have a shapefile of the crime data in the NAD 83 StatePlane California V FIPS 0405 (US Feet) spatial reference system saved in your working folder.
Next use the Project tool to create a copy of the data with the NAD 83 UTM Zone 11 spatial reference system. Add the layer with the correct spatial reference to your Table of Contents and remove the old version.