Common project pitfalls, starting with the most common:

  1. 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.)
  2. 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.
  3. 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.
  4. 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.
  5. 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.