ESRI ArcInfo Coverage
Okay. When I started working with ESRI software they were flogging the "Personal Geodatabase", which stored its data in a Microsoft format called "Jet". Then they moved on to the "File Geodatabase".
Way back before either of those, they used a format called the "coverage". It stores its data tables in a database format called "INFO". Hence the name "Arc/INFO".
A shapefile can only hold one file, with spatial and attribute data of one spatial type (such as point, line or polygon).
Coverages are more like the geodatabase formats in that they are containers that can hold any number of spatial and non-spatial tables.
(If you have a copy of it) and you start a command line session by typing "arc", then you can launch INFO and manipulate tables in coverages directly.
Format of a coverage
I don't know the right terminology yet. Bear with me, while I make up my own.
A "workspace" is a folder that contains an "info" subdirectory and usually a text file called "log".
The info folder has a zillion files with names like "arc0000" and extensions "nit" and "dat". I think it's used to keep track of coverages in the workspace, because if you move a coverage with 'mv' command it won't work. You have to move them with arc "copy" command.
A "coverage" is a folder in a "workspace". The name of the folder is the name of the coverage. The folder contains a bunch of files that store the tables that are in the coverage. Tables can hold spatial and non-spatial data. There is a "log" file in the coverage folder too.
"Log" files are interesting because they tell you who did what when, for example,
20180323 845 0 0 0bwilson append tmpbearingan ANNO.igds ALL
Projections
Coverages use a file called "prj.adf" to define the projection. It is a format that's totally different than the projection files used with shapefiles.
I discovered today that you can "define projection" on a coverage by copying the prj.adf file into the coverage folder, just like the trick of copying and renaming .prj files with shapefiles.
This does not change the data, it just tells ESRI that the file has a defined projection.
So if you KNOW some coverage is in a given projection but it has no prj.adf, just copy it in from one that is correct.
My prj.adf file for Oregon North has this in it.
Projection STATEPLANE Fipszone 3601 Datum HPGN Zunits NO Units 3.2808398950 Spheroid GRS1980 Xshift 0.0000000000 Yshift 0.0000000000 Parameters
