Opening and Troubleshooting Georeferenced Locality Data in ArcMap
1. When opening ArcMap, select an appropriate map file to get you started. To get a map you can click the Add Data Tool (yellow diamond with + sign in it on the toolbar) and select a map from the appropriate file. To obtain a world basemap, for example, you can navigate to :C\GIS\Data_Layers\world” and choose World Map.lyr.
2. ArcMap is a finicky program, but rarely tells you what’s wrong. For this reason, it is essential to follow some very simple rules while preparing your file of georeferenced locality data for input into ArcMap. First, make sure that the file name (and the names of the folders that contain it) has NO SPACES. If you need to separate two words us underscores instead of spaces (e.g., “cybotes_localities.csv” rather than “cybotes localities.csv”). Second, be sure to close the .CSV file in Excel. ArcMap will not open a file if it’s open in another program.
3. To import a .CSV file with locality information into ArcMap you must go to the Tools menu and select “Add XY Data”. Select the appropriate .CSV file when prompted. After selecting your file, “longitude” and “latitude” should appear in the X and Y fields. If nothing appears in these fields there is likely something wrong with your input file. Do a bit of troubleshooting on your .CSV file to make sure you don’t have data out of place or problematic characters (e.g., spaces or dashes) in your file or file name. In the Description Field, the coordinate type can be selected after clicking Edit. Do this only if you know that all of your data points are in one format (specifically WGS84). After you’ve completed this step, your data points should appear as a new layer in your ArcMap file.
4. Once the data points are plotted in ArcMap, you can begin looking for possible problems. The most commonly observed problems are:
(1) Datapoints that are way outside the expected range of your species (e.g., a Cuban species plotted in Africa). To find these data points you may need to zoom to the extent of your point locality data layer. These types of problems are generally due to missing minus signs or other basic errors with georeferencing and tanscription of the data.
(2) Data points that are outside the range of the species, but not dramatically so.This often results from low resolution georeferencing efforts or taxonomic changes.
(3) Datapoints thare are in the ocean. This is a common result from low resolution georeferencing efforts.
5. Once you’ve plotted your data points in ArcMap it is important to remember that you cannot move the source file without losing this data in ArcMap.
Posted by Courtney Higgins & Rich Glor – Feb. 8, 2008