Spatial Error Related to Datums and Projections

Adding XY Data using the ArcCatalog Window

Table of Contents

  1. Spatial Error Related to Datums and Projections
  2. Skill Drill: Setting Up Your Workspace
  3. Skill Drill: Downloading Data from Natural Earth
  4. Skill Drill: Connect to Your Workspace Folder in ArcMap
  5. Creating a File Geodatabase
  6. Creating Feature Classes from Shapefiles
  7. Adding XY Data using the ArcCatalog Window
  8. Skill Drill: Creating Indicatrices Using the Buffer Tool
  9. Evaluate Distortion Patterns in Map Projections
  10. Measuring Scale Distortion
  11. Skill Drill: Evaluate and Measure Distortion
  12. Troubleshooting Datum Shift
  13. Repairing Corrupted Data Using the Define Projection Tool
  14. Skill Drill: Repairing Incorrect Coordinate System Definitions

Previously, you learned how to add XY data to ArcMap using the File menu and choosing Add Data, Add XY Data. This procedure creates a representation of the data on the map as an Events layer. An Events layer is a temporary representation of the data. It might look like a regular shapefile, but it does not have a database. A depiction of the data is useful for readers that may want to view the data before making a permanent file. In this step, you do not need a temporary representation. Instead, you use the ArcCatalog window to add XY data as a feature class in your geodatabase.

Download the following CSV file, which is shared through a Google Drive link. After downloading, copy and paste the file to your original folder: Tissot’s Indicatrices centroids

Take a moment to view the contents of the file using Microsoft Excel. As you can see, it consists of a table with minimal information (Figure 2.20). There are only two fields, longitude, and latitude. The values are in degrees represented by plain integers.

Figure 2.20: To work with GIS data, the first row of a CSV table must contain the field names.

Other than the latitude and longitude coordinates, the CSV table does not contain any additional spatial information, such as the geodetic datum. To properly align the data, you must be sure to correctly define the datum from which these geographic coordinates were derived. In this instance, the geographic coordinates come from WGS 1984 the datum most commonly used by GPS receivers and the internet.

Though WGS 1984 is the most frequently used datum for GPS receivers and the internet, you should always check the necessary documentation when using a new data provider to make sure you assign the correct datum to the latitude and longitude coordinates.

In ArcMap, refresh the original folder to be sure that the CSV file appears in the Catalog Tree. When you see the Tissot’s Indicatrices centroids CSV file, right-click on the file and select Create Feature Class, then From XY table (Figure 2.21).

Figure 2.21: Be sure to right-click on the CSV file to see the correct contextual menu.

When the Create Feature Class From XY Table window appears, the longitude should automatically appear as the X field, and the latitude should appear as the Y field (Figure 2.22). If these fields do not appear, you should be able to use the drop-down menu and select them.

Figure 2.22: ArcMap automatically locates the fields in the CSV file that represent the XY coordinates.

Next, you must specify to which spatial reference system the XY coordinates belong. Click the button that says Coordinate System of Input Coordinates (Figure 2.23).

Figure 2.23: ArcMap does not have enough information to determine to which spatial reference the XY coordinates belong. You must manually indicate the correct spatial reference.

When the Spatial Reference Properties window opens, expand the Geographic Coordinate Systems folder. Next, expand the World folder. Scroll down and choose WGS 1984 (Figure 2.24). When ready, click OK.

Figure 2.24: Your Spatial Reference Properties window should look like the image above.

The output of the Create Feature Class From XY Table window should already be set to your World Data geodatabase (Figure 2.25). However, check to make sure the Save as Type option is set to File and personal geodatabase feature classes by clicking the yellow file folder icon.

Figure 2.25: If you set your World Data geodatabase as the default, it should automatically appear as the output location for any tool you use in ArcMap.

Leave all other default settings and click OK. When the geoprocessing is complete, you should see the new feature class in your geodatabase (Figure 2.26). When ready, add the new feature class to the map.

Figure 2.26: A new point feature class appears in the geodatabase.