# Why latitude/longitude and not the other way round?

When you google "latitude/longitude" you get 10 times more results than "longitude/latitude". This I find very confusing as "x/y" seems 20 times more common than "y/x". But on a map Latitude is on the Y axis and longitude on the X.

Maybe I'm just venting, but maybe I'm missing a clue that makes all this madness logical.

Any explanations?

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.

• And as for why x is usually referenced before y, that has to do with the mathematical convention: when referencing Cartesian coordinates (i.e. the xy representation of latitude and longitude, which are not technically Cartesian themselves) the x-coordinate is typically referenced first. Dec 19 '11 at 16:56
• martin f - Reasons for the edit to my answer? I really think the second part is as relevant as the first, unless you have a reason to disagree. Dec 22 '11 at 2:02
• martin f - I just read your reason for editing my initial answer. I disagree. I believe historically, Lat could only be derived after accurately establishing Lon. Dec 29 '11 at 3:58
• I'm afraid I have to downvote this reply as a result of the edit, Don. @mpeterson was correct that coordinates are independent. A natural reading of your phrase "longitude is based on latitude" is that finding longitude (historically) required knowing the latitude, but that assertion is wrong. Some clarification of what you mean by "based on" therefore is in order here. Dec 29 '11 at 5:13
• OK, a little more research says I was wrong. When I answered 9 months ago, I had just read "The Story of Maps" by Lloyd Brown, and mistakenly concluded lat had to be determined before lon could be calculated. However, lon can be determined using only time dif from UTC. No need to know lat. I re-rolled back to revision - 2. Dec 29 '11 at 13:34

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.

• Engineering, geography, mathematics, astronomy, and physics use several different conventional orderings (and names) for spherical coordinates. This suggests there is something arbitrary about your reasoning. Dec 29 '11 at 5:15
• I guess I wasn't clear. My main point is that since lat/lon are spherical coordinates, there's no reason they should match the ordering of Cartesian (xy) coordinates. Furthermore, there are disciplines in which the order of the spherical coordinates match lat/lon, and hence could be the origin the OP is seeking. Dec 30 '11 at 0:47
• Lurking here is the concept of orientation: the x-y convention establishes an orientation for the plane. Similarly, lat-lon establishes an orientation for the sphere's surface. With such conventions in effect, all projections that look orientation-preserving (that is, they do not turn shapes into their mirror images) require orientation- reversing calculations. Thus there is a strong reason to prefer long-lat as the order. A good answer therefore would adduce information, probably historical in nature, that clarifies why a contrary convention ever became popular. Dec 30 '11 at 14:25

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".