Is the ESRI ArcGIS definition of California Albers projection using units of feet correct?

Question

There is a map projection promulgated by the government of the state of California and recommended for use in certain state and municipal regulations. It is an Albers Equal Area projection with origin at a convenient point amidst the state and appropriate false easting and false northing. From what I can tell, the projection was first defined for use with linear units of meters. It's listed in ArcGIS under State Systems, NAD 1983 California (Teale) Albers (Meters) with well-known identifier (WKID) 3310 from European Petroleum Survey Group (EPSG). At least, that's how it appears in the ArcGIS 10.4 catalog of projections. The list of projections has other entries and WKIDs too for very similar projections. Anyway, ArcGIS displays the list of parameters in the projection definition. Among the projection parameters is a false northing value of –4000000 meters. So far, so good.

The ArcGIS coordinate system list also includes one labeled NAD 1983 California (Teale) Albers (US Feet) with WKID 102600, on the authority of ESRI. Units of feet are pretty common still in the US, so this projection sounds like a fine one I should use. But when I examine the projection's definition and parameters, there's something odd. The projection's linear unit parameter is the US foot. No surprise there. But the false easting value is –4000000. That's –4000000 feet, I presume?

Shouldn't the false easting be in terms of US feet, which would be something like -13123333 feet? (The factor is 3.28 or so, the meter-foot conversion).

Answer 1

Disclosure: I work for Esri as a product engineer focusing on coordinate reference systems and transformations. Disclosure 2: I'm on the subcommittee that maintains the EPSG registry.

You are correct. We have the same value for the false northing whether the unit of measure is US survey feet or meters. That is incorrect. The false easting/northing parameter values should be in the unit of the coordinate reference system.

However, the original meter-based definitions were added in ArcGIS 9.2. The US survey foot versions were added in ArcGIS 10.2 which was released 6 years ago in August 2013. At this point, I don't think it's worth it to 'fix' the feet versions.

The false easting/northing parameters were originally used to ensure that all coordinates are positive. It's not an issue now that computers do the calculations and (usually) the labeling.

They've also been used to differentiate between different versions of a zone like in the state plane coordinate system. Many zones changed the false easting and/or false northing values when the NAD83 set was defined.