Why latitude/longitude and not the other way round?

I'm not an expert in this area, but I have done some reading on the subject, particularly on its history. I think the reason is: Accurate measurement of latitude came first as it was based on astronomical measurements. Longitude was not accurately measurable until a highly accurate time measuring device was developed.

While this has always bugged me, I had never stopped to think about it too much. Perhaps the solution lies in recognizing that this is a false comparison. We are used to seeing latitude and longitude marked on paper maps, tempting us to think of these as planar (Cartesian) coordinates. However, they are not; the paper (planar) map is a projection of spherical coordinates, and spherical coordinates are generally written as radius, inclination, and azimuth (at least in physics.) In fact, the order radius, inclination, azimuth is codified in ISO 31-11. Geographers don't need the radius (or to the extent they do, they use elevation/altitude, which is the deviation from the nominal radius of the earth), so we just have inclination (latitude) and azimuth (longitude). From this perspective, latitude/longitude is perfectly rational.

Latitude was first used as a measurement in around 600 BC by the Phoenicians using the pole star as a reference. Longitude did not come into general use until the invention of the Harrison marine chronometer in 1760. International Standard ISO 6709 quotes "Latitude comes before longitude".