Projections

[Kieran J. Ames]

List,
I want to try projecting some planimetric data with my own data. Would
someone review the following and tell me if I'm on the right track?

In a mapfile, I can state an output projection at the beginning of the
mapfile, outside of any other class or layer section.
I have planimetric raster files that I want to use as a basemap. They
are UTM, NAD27, Zone18. I have therefore put the following into my
mapfile:
PROJECTION
  "proj=utm"     # I understand this
  "ellps=clrk66"# I understand this
  "zone=18"     # I understand this
  "north"       # No Clue!
  "no_defs"     # No Clue!
END

I want to add point and line data on top on the basemap, but they are in
Decimal Degrees. Therefore, for each DD layer, I need to add the
following:
PROJECTION
"GEOGRAPHIC"
END
That will make the LAT/LON data line up properly with the basemap.

How am I doing?

BTW, can someone point me to documentation on the PROJ4 Projection
arguments? I can't fine anything on the use of "north" and "no_defs" or
any of the other arguments I've seen in the archives.
Thanks much for any input.
Kieran Ames