New users to ArcMap frequently experience lost data and corrupted maps due to the complicated ways that ArcMap references data and layers. Given that the connections between a ArcMap Map document and its data are references to locations of files on a network, if the Map file or one of its data sources has been moved, the connection with the data might be lost (hence the little red exclamation point...e.g. the data is not located where ArcMap thinks it is). You will need to change the data layer's source in ArcMap in order to restore the data reference (see below).

How do I avoid this problem? The default behavior of Arcmap is to store Absolute Path References (the entire path to the data, including drive letter, is saved). In this mode, you may move your map documents wherever you want to; as long as the data aren't moved and/or you haven't changed the drive letter of an important mapped drive, the references will work.

A more efficient practice is to use relative paths though. If you have all of your data and maps within one folder, (which is a good way to work if you are keeping backups of your work), you can set ArcMap to store Relative Path references (in ArcMap select File > Map Properties > Data Source Options). This will allow you to move this one folder around wherever you want, even to a CD, and you won't lose a connection to the data references. Below are some simple rules to use:

• Never move GIS data using Windows Explorer, use only ArcCatalog.
• Always keep the datasets, layers and Map files you are working with in a single folder in a specified directory. It is Ok if the data are in subfolders as long as you don't change the relationships among the subfolders and files.
• Always set your Map Properties->Data Source Options to store relative pathnames for every map file that you make.
• Never use spaces in filenames or in the names of directories. This means that you should never store data in your Documents and Settings folder or on the Desktop. This will cause problems with Spatial Analyst.
• When you back up your work, back up your entire working folder.

Steps to change a layer's data source:

1. Right-click the layer in the ArcMap Table of Contents and select Properties
2. Switch to the Source tab.
3. Click the 'Set Data Source' button.
4. Navigate to the location of the new data set, select it, and click the Add button.
5. Click the Apply and OK buttons on the Layer Properties dialog box.

ArcMap supports project on the fly, meaning that you can make a map in one projection (referred to as a coordinate system) and have your data stored in any number of different projections. The projection of your map is the dataframe coordinate system. There is only one coordinate system for your dataframe. The projection of your data is the data coordinate system. There can be as many data coordinate systems as there are layers in your map.

To check your data and dataframe coordinate systems in ArcMap:
Check your dataframe coordinate system by double clicking on the dataframe and selecting the Coordinate System tab.

Check your data coordinate system by double clicking on a layer in the ArcMap Table of Contents and selecting the Source tab.

Instructions provided describe how to salvage a corrupt shapefile. Shapefiles sometimes become corrupt. Common causes of corruptions are a computer crash while saving edits, adding illegal geometry; for example, bowties, modifying the attribute table in another software, for example: Microsoft Excel. The entire ammount of possible casues for corruption are beyond the scope of this document. If the steps in this document do not salvage the shapefile, revert to the back up.

There are several ways to salvage a corrupt shapefile. Verify a back-up of the data was made before attempting any of these options.
Use the Check Geometry tool in ArcToolBox > Data Management Tools > Features. Problems with the data are reported while the tool is executing, or in the output table. View the output table after execution. An empty table indicates that the tool found no bad geometry. If bad geometry is reported, use the Repair Geometry tool in the bullet below.

• Try using the Repair Geometry tool in ArcToolBox > Data Management Tools > Features.
• Download and use the cleanshapefile utility from the Related Information section below.
• Attempt copying the data to a geodatabase. Afterwards, also try copying it back to a new shapefile.
• If the data is on a network drive, copy it to a local drive. If the data is on a local drive, try copying it to the root of the primary drive; for example, C:\
• Check for illegal field names in the attribute table. Field names can only have 10 characters. Field names MUST start with a letter. Field names must not contain any spaces or special characters, except for the underscore character.
• File names must not contain any special characters, except for the underscore character. Generally speaking, spaces in shapefile names work in ArcGIS 9, however for testing purposes rename the shapefile to not have any spaces.
• Remove all index (spatial, atrribute and geocoding) and meta data files in windows explorer. That is, remove all files except, the .shp, .dbf and .shx. Verify a copy of these files has been made before removing them.
• Try opening the shapefile on another computer.
• Try opening the shapefile in another software, preferably ArcView 3.x.
• Try bringing the data into another feature class either by using the simple data loader or by copying and pasting in an edit session.
• If the data is still not repaired, and steps 1 or 2 above reported the feature ID's of the bad records, try manually removing them in an editing session.

Yes, but Geodatabases built prior to ArcGIS 9 do not support some of the new and improved functions of ArcGIS 9, such as Geodatabase rasters and improved annotation.

No, changes to the Geodatabase prevent backward compatibility. The following error will occur in both ArcCatalog and ArcMap if you try to open a version 9 Geodatabase in 8.x:

Failed to connect to database. This release of the GeoDatabase is either
invalid or out of date. [Unknown GeoDatabase release.]

Shapefiles that can be viewed with no problems in ArcGIS 8.3 cause the following error when viewed in ArcGIS 9.0:
"Error opening feature class. Number of shapes does not match the number of table records."

Between ArcGIS versions 8.3 and 9.0, ESRI tightened the requirements on what classifies as an acceptable shapefile within ArcMap and ArcCatalog thus causing this error.

Select one of the following options to solve this issue.
Download 'Shapefile Repairer' from ArcScripts.
Download 'Shapefile Checker' from Andrew's ArcView Page.

Folders containing many files may slow down the ArcMap Add Data browser.

This happens because before adding data, the Add Data process must search through folders and subfolders to verify the data is geographic. The time this takes depends on the number of folders.

To workaround this drag and drop the data or layer from ArcCatalog into ArcMap.

In ArcMap XY data can be exported to a shapefile, or as a feature class in a geodatabase. If the coordinate values for some of XY data records are blank, that is the X or Y values are null, and you export to a shapefile, the exported shapefile will contain points with coordinate values of zero.

To workaround this issue exclude XY data records with null coordinate values when exporting to a shapefile. You can export null records to a personal geodatabase.

The .aux extension indicates an auxiliary file used to store information not normally supported by the particular raster format. The TIFF file format, for example, does not store image statistics, so statistics generated by ArcGIS are stored in an .aux file with the same prefix name as the .tif file

The .rrd extension indicates an pyramid file used to speed raster display. When a raster has to be represented in a series of reduced/increased resolutions, a “pyramid” is built for that particular raster. A pyramid is a series of reduced resolution representations of the dataset, mainly used to improve the display performance of rasters when one is not working with the pixel information at full resolution. It conatins a number of layers, each resampled at a more generalized level. Thus each level of the pyramid is a resampled representation of the raster at a coarser spatial resolution.

The data is viewable without this and the auxiliary file, however loading times will be slower.

There a couple reasons why the spatial reference of an image defined in ArcCatalog or ArcToolbox isn't recognized in an ArcMap dataframe. This is generally related to one of two things, the world file or pyramid layers.

World files are small text files that contain the size and position (georeference) information for an image. A typical world file might look like:

20.154   <the dimension of a pixel in project units in the x direction>
0.000     <rotation term for row>
0.000     <rotation term for column>
-20.154  <the dimension of a pixel in project units in the y direction>
424178  <the x coordinate of the center of pixel 1,1 (upper-left pixel)>
4313415 <the y coordinate of the center of pixel 1,1 (upper-left pixel)>

World file formats have different extensions for different image types. When an image is read (using menu File | Open or File | Insert File), ArcMap looks for a matching world file using the following extensions.

*.tfw - world file for tif image
*.bpw - world file for bmp images
*.jgw - world file for jpg

If no world file exists, the image is inserted so that the upper left corner is in the center of the screen and the pixel size is set to one. Despite defining a projection, the lack of a world file (or a misnamed world file) will cause the image to not display correctly in ArcMap.

It should also be noted that GeoTiff files are Tif images with georeference information embedded in them. ArcMap will read GeoTiff files. GeoTiff files (such as some USGS DRG’s) strictly do not require a world file because they already have that information embedded in the file. In this case if a world file exists, the information in the world file will override the embedded information.

When a raster has to be represented in a series of reduced/increased resolutions, a “pyramid” is built for that particular raster. A pyramid is a series of reduced resolution representations of the dataset, mainly used to improve the display performance of rasters when one is not working with the pixel information at full resolution. When pyramids are created the spatial reference of the dataset defined at the time of pyramid creation is hard-coded into the pyramid layers.

If pyramid layers are built for a dataset before defining its projection, setting the spatial reference will have no affect in ArcMap becasue the pyramid layers (with the hard-coded projection, e.g. unknown or wrong) are overriding the defined projection. To correct for this, delete the .rrd and .aux files of the dataset using Windows Explorer, redefine the spatial reference information in ArCatalog or ArcToolbox to the correct projection, and then build pyramids

Note: The data is still viewable without the pyramid and the auxiliary file, however loading times will be slower.

ArcGIS 8.x and 9.x do not support editing raster tables nor adding fields to raster tables. Therefore, when opening a raster attribute table, the Start Editing option on the Editor toolbar is grayed out, and so is the Add Field option on the Options menu of the raster attribute table.

To edit attribute tables for grids, ArcInfo Workstation or ArcView 3.x can be used.

A second approach is to use ArcObjects programming to add a field to the GRID VAT, delete a field from the GRID VAT, or update the VAT. An alternative option, for display purposes only, is to join fields to a raster layer attribute table using the following procedure:

1. Right-click the raster layer in the table of contents of ArcMap.
2. Point to Joins and Relates.
3. Click Join.
4. Follow the instructions in the dialog box.