Hi All

Thanks to Bill Huber, Tim Loesch, Micha Silver, Sven
Lautenbach and Thorsten Behrens for their solutions.
Basically everyone told me to use the CON or SETNULL
requests.  My original question is below, followed by
one of the responses (from Thorsten).

---My original question----
I have a layer that I want to use in Map Calculator to
do some basic math.  My problem is with the lake in my
layer.  I'm trying to do some surface runoff
calculations and I don't want the cells in the lake to
have any values after the calculation is complete
(because we will then be reclassing the layer based on
the calculated results).  Because of the way the
equation works, I can't just set the lake cells to a
specific value to end up with zero in these cells.

For all those Avenue programmers out there, is it
possible to first search the layer for a specific cell
value (say 0) and assign a value to it such as 1000
(which would be well out of our calculation results),
and then perform a calculation on the remaining cells?
 Or can you ignore particular cells while doing a
calculation (based on the fact that they are equal to
something, say 0)?

p.s.  I've also been trying to assign NO_DATA to these
cells, but I'm not having any luck.  Our layer already
has a mask set (surrounding our study area), so if I
did somehow reclass the lake as no_data, I'm assuming
that there isn't a way we could distinguish between
the two?

---Answer from Thorsten Behrens----
what you need is the con-request, setnull and isnull.
The examples listed below show how they work:

The line of code below converts cells with a value of
0 to 1000:
outGrid = ( inGrid = 0.AsGrid).con( 1000.AsGrid,
inGrid)

The line of code below converts cells with a value of
1000 to No Data:
outGrid = (inGrid = 4.AsGrid).SetNull(inGrid)

The line of code below converts No Data cells to the
value of 1000.
outGrid = inGrid.IsNull.Con(31.AsGrid, inGrid)

The lines of code below convert cells with a value
lower 0 to 0:
outGrid = ( inGrid > 0.AsGrid).con( inGrid,  0.AsGrid)
outGrid = ( inGrid < 0.AsGrid).con( 0.AsGrid,  inGrid)


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