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.
An image of the Los Angeles County GIS Data Portal

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.

An image of the Crime data download page

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.

An image of the crime csv table
A CSV table of crimes in Los Angeles County.

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.

An image of the Add XY data window for crime data
You can locate the spatial reference ArcMap will use under the Description. To re-define the spatial reference, click on the Edit button to select the correct spatial reference.

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.

An image of the Warning Dialog Box in ArcMap.
The ArcGIS software will remind you that you will still need to export the events layer to create a permanent shapefile that includes database functionality.

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.

An image of the crime data events layer
An events layer is temporary and should be exported as a shapefile.

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.

An image of the project tool.
The Project tool never alters the original data. It creates a copy of the data with a new spatial reference system.