My primary problem with this section of the lab assignment was re-projecting one DOQQ. All four came from the same source, and I thought were in the same projection. But there is apparently a critical difference between GCS_North_American_1983 and GCS_North_American_1983_CSRS. I didn’t notice the minor difference at first, until the latter could not be re-projected. ArcCatalog closed abruptly each time I tried to perform the operation. I eventually downloaded other DOQQ files and had no problem.
I added the USGS Quad background, which I clipped to the county boundary. I did not have to clip my other layers (I was able to download already clipped layers for my county), and wanted to practice that part of the lab.
I was eventually able to research CSRS, and discovered it is the Canadian Spatial Reference System, which is a 3-dimentional system. It includes data not only on height (elevation?) but gravity and earth rotation. It’s no wonder ArcCatalog choked on it.
I don’t know why one of a set of four DOQQ files was in that format, unless LABINS is in the process of converting to that format.
