Does Y mean latitude and X mean longitude in every GIS software?
I am using Mapinfo and it has Y as latitude and X as longitude. Is that the same case for all mapping software? As for any country their respective value is multiple of 1 or -1. So for Nepal can I say it is on positive side +1 for both latitude and longitude? And for USA to be +1 Y and -1 X.
Latitude is the Y axis, longitude is the X axis. Since latitude can be positive and negative (north and south of the Equator), and longitude can be as well (negative west of Greenwich and positive eastward) when the -180 to +180 longitude system is use. Hence the four combinations of positive and negative are possible depending upon where you are located on the globe.
You will appreciate an earlier thread that discusses this question more generally: http://gis.stackexchange.com/questions/6037/latlon-or-lonlat-whats-the-right-way-to-display-coordinates-and-inputs.
Surely the mathematical x,y axes are at right angles to each other. Latitude & longitude are not.
@user84263 - in a *Euclidean* geometry, axes are at right angles, and lines that are constant in one coordinate are all at right angles to lines of the other coordinate. On a non-Euclidean surface, as you point out, this cannot be the case. Nevertheless, a spherical or ellipsoidal surface can be defined by two coordinates, call them x/y or longitude/latitude as you wish. Begin at a given point on the surface, and rotate that point independently around two perpendicular axes of rotation. This yields a pair of "axes". Along one axis, x is zero. Along the other axis, y is zero.
No, for example when talking to a GeoServer WFS (or any other compliant WFS) the axis order depends on if you ask for version 1.0 or 1.1 of the spec in EPSG:4326.
The original spec had longitude,latitude order. This is more of a software-oriented view as it matches up with [US-centric] x,y order. This doesn't match the ISO standard, so various later specs have changed the order to latitude,longitude. This order should be used when displaying or transmitting the values, they don't have to be stored that way. Not everyone uses x,y as the labels for easting,northing. Some people use y=easting,x=northing. For projected data, the coordinate reference system defn should specify the axis order and labels.
@mkennedy Although the US convention may be (long, lat), that does not make such a convention "US-centric." This actually is the *international* and very long established convention in mathematics and physics. It is based on the concept of orientation of a coordinate system in which (long, lat) agrees with the conventional positive (x,y,z) orientation of 3D Cartesian coordinates when an outward-pointing normal direction (*i.e.*, "up") is used for the third coordinate on the sphere.
For ESRI its almost always going to be:
Lat = Y Long = X
It's easy to get backwards. I've been doing this for years but still need to think about it sometimes.
On a standard north facing map, latitude is represented by horizontal lines, which go up and down (North and South) the Y axis. Its easy to think that since they are horizontal lines, they would be on the x axis, but they are not.
So similarly, the X axis is Longitude, as the values shift left to right (East and West) along the X axis. Confusing for the same reason since on a north facing map, these lines are vertical.
I'm mildly dyslexic so I always need to pause and think about it for a brief second when displaying new x/y data. Hope this helps.
This is confusing: by definition, "horizontal" means *level*: such lines extend from side to side, not up and down. Horizontal lines are lines of constant latitude; latitude varies in a vertical direction: your description could be read as just the reverse. You might find the historical reason for these terms to be of interest.
Well explained. I never quite understood why the relation between (lat, lng) and (y, x) was "inverted" like that.
@emyller, because azimuth is North oriented, clockwise. Trigonometric functions based on the azimuth assume unexpected behavior if the positive _x_ coordinates towards the North and positive _y_ towards the East are not considered. Geodesic and topographic calculations are carried out in this system. Although they are later translated into the conventional (Easting; Northing) system for other purposes.
Does this mean that esri does not use EPSG authority codes for identifying Coordinate systems, as nearly all of the geographic systems have first axis as latitude
This is probably the StackOverflow-answer I visit most often... :)
X and Y are variables that can change for different purposes. For example: You may want to know the wind-speed, and you could use a sailboat's speed to know how fast is the wind going, so we can say: the sailboat = X and wind = Y. But it could also be that, you don't know how fast is the boat going and you can find its speed by knowing the wind-speed so now wind = X and sailboat = Y. However: The Equator, Prime meridian (at Greenwich), North and South, and Latitude and Longitude don't change. From the Equator to the North pole we measure Latitude 0° to 90° respectively, from the Equator to the South pole we measure 0° to -90° respectively. From the prime meridian at 0° we measure West up to -180° and East up to 180°. Sometimes -+ are replaced with West and East so that: -81° and 81°W mean the same thing. ESRI corporation regularly use X as longitude and Y as latitude.
In this question "X" is shorthand for the first element of an ordered pair of coordinates and "Y" for the second element.