Thursday, July 16, 2015

What do you do when your shapefile won't display in ArcMap?

From time to time I get e-mail questions from colleagues about what to do about the terrible and dreaded red exclamation in ArcMap.  Here are  a couple of pointers when working with shapefiles and ArcMap documents (MXD files).  First off some general advice on what to do when you get the red exclamation make:

1.  The shapefile is in the same location but the drive letters on the computer are mapped differently (e.g. Z: vs. X: vs. whatever).  If knows where it is located at it is as simple re-pathing the data.  In the Table of Contents (left panel usually) right click on the layer and go to properties.  The click the source tab followed by the set data source button.  Navigate to the file and it should update.  All other files in the same folder will be updated.  If you're using different logins then some of the locations that might be accessible to you wouldn't be to him and visa versa so that is one good reason to always save files on the network to locations that he/you can always both access.

2.  If the file was moved use the same procedure as above but navigate to the new location.

3.  Shapefiles are composed of many different files that need to be kept together.  At a minimum there is a .shp, .dbf, and .shx, but there will also be a .prj and probably a .sbn.  These files need to be kept in the same folder at all times.  If one or more of them gets moved you should move it back.

4.  As with #4 if one of those files gets deleted or corrupted you are out of luck.  Most like this isn't the case.

and some general data management tips:

1.  Always use the catalog tab in ArcMap to move, copy, or delete files.  It'll treat all of the files that compose the shapefile as a single entity.

2.  Always place your GIS files in network accessible locations and avoid the local hard drive, dektop, my documents, or temporary places that might get wiped out periodically.

3.  When editing shapefiles save frequently.  The more the better since ArcMap doesn't have an auto-save feature.

4.  Set relative paths for your ArcMap document.  File - Map Document Properties - and check 'store relative pathnames to data sources'.  There is even a setting to make this the default.  Customize - ArcMap Options - General - check 'make relative paths the default for new map documents'.

5.  Keep good mental notes where you place files and pay attention when writing outputs.  If you are ever in question go to the layer properties and view the file path or use the list by source tab in the table of contents (looks like a silver can with a yellow arrow).

6.  Practice good data management skills.  Delete old, unnecessary, duplicate, or corrupt files periodically.  Elevate final products to folder locations with really clear and memorizable paths so that you or anybody else can find your way back if necessary.  Give files really specific names that describe their purpose and avoid default names like Export_Output.  If you are going to have multiple users or multiple dates consider using suffixes with your initials and the dates to help keep track of file versioning.

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