How Export To Interchange File (Coverage) works

The Export To Interchange File tool creates an interchange file to transfer coverages; INFO tables; text files, such as AML macros; and other ArcInfo Workstation files between various machine types. An interchange file contains all coverage information and appropriate INFO table information in a fixed-length, ASCII format. It can be fully or partially compressed and decompressed ASCII depending on the Export option used.

There are many ways to use Export. One way is to transport a coverage and its associated INFO tables. This is done using the keyword COVER for the first argument. Another way is to transfer an INFO table. In this case, any INFO pathname/username can be used to specify the INFO table to be exported. This option is invoked by using the keyword INFO for the first argument. Export may be used with the TEXT option to transfer key files, AML macros, and other text files.

Once Export is used, the interchange file can be transferred by tape to another machine where Import can be used to recreate the coverage, INFO tables, text files, and so on.

The Import and Export commands can also be used to back up individual coverages to tape for archiving (as opposed to backing up entire user workspaces). For example, individual coverages corresponding to map library layers within a single tile (for example, map sections) can be archived to tape and restored to disk as needed.

The following is a checklist of what issues must be dealt with when taking an export file from one platform to another:

• Run Export with the NONE option. This creates noncompressed ASCII files that are easier to handle than fully or partially compressed ASCII files. Fully or partially compressed ASCII files can cause problems when transferring data across different platforms, such as UNIX ARC/INFO to PC ARC/INFO, and vice versa.
• Always Import the ".E00" file back into the host platform before transfer to make sure that the ".E00" file is error free. Export does not check for errors within the coverage; Import does. So if changes need to be made to the coverage, they must be done at the original site, not to the ".E00" file.
• Use the {max_lines} option in Export to create more than one volume for the export file. A value of 20,000 will create volumes that are able to fit onto a high-density floppy disk. Use a finite number so that at least two volumes are created. Transfer both files to the other platform and make sure they are in the same directory when using the Import command. Import automatically searches for the next volume when more than one volume is created.

Note:

Exporting a grid can result in an export file much larger than the original grid, even when Full compression is used. This is because each grid cell must be represented in the export file in ASCII format, which is less efficient than the grid's binary format. Also, integer grids are stored in a compressed format, which cannot be maintained in the export file.