I swear that every day I use ArcGIS I seem to find a new problem. Here is the latest.
Running ArcGIS basic 10.3.1 on WIndows7 VM under parallels on MAcbookPro.
I have a feature class that was created from Business Analyst BDS
Demographic Layer of Census Block Groups (CBG) by removing many of the fields
which were not of interest and by limiting the CBGs to only those in 3 states (spatial join).
As a result of this data reduction two new fields are added: Shape_length and Shape_Area.
I was puzzled that the values in Shape_Area did not remotely agree with a BA field named
Land Area, not did the ratio between them seem to be any sensible conversion ratio
like SqMiles/SqMeters. So I used a tool in ArcCatalog,
Tools=>Data Management Tools=> Features=>Add Geometry Attributes
which enables me to calculate something called the Area Geodesic.
I choose as units square meters, it calculates the result, which indeed did
not agree with the existing Shape_Area field.
OK. So just to check I thought I would just run the tool once more. I delete
the field just calculated and invoke the tool again. Now the tool dies.
1. Whenever one selects a subset of features from a data source and exports those features
to a new feature class (mine are all in a file geodatabase), new fields are added. In my case
the features are polygons, and the new fields added are Shape_Area and Shape_Length.
Why? If I wanted those fields I could use tools to calculate them.
2. What is Area Geodesic anyway? Is it more or less the same as the area assuming flat earth?
(for a small region, say the size of a census tract or block group)
3. The values in these fields did not appear to be correct. Because quite a bit of time has elapsed
since this feature class was created I cannot remember details such as whether the layer
was re-projected to a different PCS or GCS. But how could the values be incorrect?
Do they change if the PCS changes?
4. It is impossible to remove these fields. The "delete" button is greyed out. Why?
I don't want them, and aren't they available as the "hidden" geospatial parameters
in a feature class anyhow?
5. If one takes the newly created feature class and make a further selection,
select by location, and export that new subset of feature, those special fields
Shape_Area seem to be created a second time. So now I have two of them!
6. The Add Geometry Tool is now failing after working the first time
I have screen captures of the results from this tool on the first (successful) invocation
and the second (and all subsequent) failing invocations. They are attached.
In the last 3 weeks or so I think I have posted to GeoNet every two days.
People must be fed up reading my stuff. (Thank you all for nonetheless
helpful suggestions) Is it just me? I can't believe I
am really doing things which put me at the bleeding edge of GIS.