Common project pitfalls, starting with the most common:
- Projection Problems: Data downloaded from various sources
are commonly in different projections. They are commonly in the Geographic
Coordinate System (GCS/latitude-longitude) and you may have a hard time creating
slopes or other results that need a Z factor setting -- the tool may not suggest
a Z factor. While ArcMap can project on the fly, many tools expect data to
be in the same map projection. This may change in the future, but is still
the case at 9.2. Your project should start by getting everything you'll
use for analysis into the same map projection. (Exception: orthophotos/imagery
are generally only used for displays, so they can remain in whatever map projection.)
- Dataframe / layer mismatch. Remember that the first layer
added to a map sets the dataframe coordinate system. Dataframe and layer coordinate
system mismatch can cause problems too.
- Geoprocessing settings: cell sizes, extent, mask. You learned
about these this semester, so apply it now. Know what cell sizes and extents
are being set in your program/model steps, and how they influence this results.
If you change study areas, a prior extent setting may lead to nothing. Remember
that models can have settings that override those of ArcMap.
- Null areas. Again, we learned about this during the exercises,
but a common pitfall in projects is not understanding where datasets have
null values and how to deal with them. You need to know the correct use of
con, setnull, isnull, and other tools that create and use null values.
- Understanding how tools work. Even if you've used a tool
before, save yourself some time in the long run by reviewing the help system
on the use of tools. You won't use that many tools, so really understanding
the ones you use will make things go more smoothly.