[GRASSLIST:197] Coastline and category confusion

[Antonios Christofides]

Hi, this is actually two related questions; let's start with the
category.

A category, according to v.digit, has a "number" (also denoted by the #
symbol) and a "label". But according to v.report, a category has a "number"
and a "description". And elsewhere (e.g. man d.what.rast) a category has
a "value" and a "label". It may appear silly to you, but if you were a
newbie trying to figure out what a category is, you might well be
confused.

So, as far as I can tell,
  category number     is the same thing as     category value
  category label      is the same thing as     category description
Correct? Now, does a category also have attributes? How do I define a
category attribute?

Now my other question: the coastline, or the contour with elevation
zero. I've digitized contours and coastline and I want to create a DEM.
But I can't figure out how to specify that a contour has elevation zero.
Category numbers are used for the elevation, and a category number of
zero means quit (in v.digit) or nonexistent in other cases. The best I
could do was to give it an elevation of -1 (doing d.what.rast on the
dem, near the coastline, gives "quant (0)" but "actual" closer to -1;
what do these things mean?)