ArcMap Showing Negative Values?
This post is an actual exaggerated account of events in the office. Names of the innocent have been protected.
I'm sitting in my office working on a way to streamline checking data from a large and terrible organization and I click on one of our links and see the worst possible thing: a negative AADT (Annualized Average Daily Traffic, basically a traffic count!).
After screaming across the aisle to the poor soul that has to fix things like this (who replied with an exacerbated "WHAT?" when I said "Hey, why are the AADT's negative on the Big Mac Bridge?" and we both checked the model output to see that, indeed, the model output claims that the AADT is positive, I started looking further into the problem.
I started with FoxPro (I may be the last person with FoxPro installed on their computer, but IT can uninstall it over my cold dead body AND after removal of my ghost) and found that the AADT should be 44,043 (in one direction).
Then I remembered that we've had this problem before, but I thought that bug was fixed (silly me for thinking multiple-year-old bug get fixed). I looked into it on the web and found a statement from one of ESRI's own indicating that the problem is with ArcWhatever* converting 5-width numbers in DBFs to be short integers (which range from -32,767 to 32,767). 44,043? Too big, so the number gets displayed incorrectly.
The fix is surprisingly simple: change the width of the field in FoxPro from 5 to 6.
Once the fix is made, the data is displayed as a 32-bit integer.
- I first saw this with a data layer served by ArcServer. Or ArcSDE. Heck, I don't know the difference, I just ask our GIS department for a REST endpoint and they take care of me and that's where I actually saw this.