How To: Identify and fix when the Add XY Data tool does not produce the correct XY event layer
This article addresses some common problems that cause the Add XY Data tool not to work or to place points in the wrong location.
The XY event layer is created using the Add XY Data tool either by:
- Right-clicking a table in the Table of Contents (when in List by Source view).
- Clicking File > Add Data > Add XY data.
- Clicking the Make XY Event Layer tool from within Data Management Tools > Layers and Table Views.
Note: This article pertains to ArcGIS versions 9.x and 10.0. Later versions of ArcGIS may contain different functionality, as well as different names and locations for menus, commands and geoprocessing tools.
The following list contains some of the potential causes for the data to appear in the wrong location during the creation of a XY Event Layer. Each cause has a corresponding solution and reason why this causes a problem for the tool:
- The coordinate system of the Input Coordinates is incorrect for the XY data that is stored in the table.
Solution: Identify the coordinate system that the XY values were originally collected in for the table. Investigate the values if the coordinate system is unknown. Geographic coordinate systems such as NAD 1983 and WGS 1984 are common and have values ranging between X: -180 to 180 and Y: -90 to 90. Use unknown coordinates if it is unknown, then use the first related link below named 'Identify the spatial reference projections or coordinate system of data'.
Reason: The Add XY Data tool must know what the original coordinate system was during the point collection in order to properly plot the points. The tool must reflect the input coordinate system and not the desired coordinate system.
- The X and Y Fields were switched or mislabeled.
Reason: It can be easy to get the names of longitude and latitude confused or just have an odd naming convention for the field names. The Add XY Data tool reads through the values and places the data based on the assignment it has for the X and Y fields. If the data is in projected coordinates and therefore not decimal degrees, it can be more difficult to determine if the fields were switched.
- There is a missing negative from the X field values when the values are decimal degrees (geographic coordinates).
Reason: For data in the US, most of the decimal degree values will be negative X and positive Y. This is because of how decimal degrees are displayed eastward and westward of the prime meridian. The breakdowns of values for each hemisphere are below:
- Northern: +Y
- Southern: -Y
- Western: -X
- Eastern: +X
- If the XY fields do not show up in the Add XY Data tool, the XY fields are not numeric fields.
Reason: The Add XY Data tool will only work with true numbers.
- The XY values are in Degrees-Minutes-Seconds.
Reason: The Degrees Minutes Seconds format is typically stored as text because it requires directions and spaces. The Add XY Data tool, as seen in the previous cause, cannot read values in text field format and they must be converted to true numbers with a decimal.
- There are problems with the data frame coordinate system or other data in the map that makes the comparison appear wrong.
Reason: Sometimes the reference data may have been stored with or assigned the wrong coordinate system resulting in the XY data appearing to be in the wrong location. The other data must be modified and assigned the correct projection. Typically, assigning the correct coordinate system or projection is done with the Define Projection tool.
- Identify the spatial reference, projection, or coordinate system of data
- Version 10 Help: Adding x,y coordinate data as a layer
- Converting and Displaying Coordinates in ArcGIS 10 Blog Post
- Version 10 Help: Define Projection (Data Management)
- Calculate Field examples