Non-geographic grids on maps

Question

There are plenty of maps around, printed and otherwise, with numbered grids that do not directly equate to real-world coordinate systems.

Typically these grids will have 0,0 in the bottom-left corner - at least, in the most of cases that I have personally seen.

This seems to be at least an informal convention. My question is whether this convention is more established?

Are map-makers just gravitating towards something that they think most people will instinctively understand, or are there additional reasons for them to follow this approach?

Background: All developer-created maps and most community-created maps in a particular computer game follow this convention. However a very small number of community-created maps have a Y-axis that goes in reverse, so 0,0 is in the top-left corner.

Not only do players often miss this, and thus misread coordinates, but even in-game tools misread these coordinates - both being one grid out on the Y coordinates.

For example, a point on the map, might be denoted as (0125, 0125) on the grid, but read as (0125, 0135) by the in-game tools.

So as a matter of curiousity, I'm trying to find out which of the following cases is most accurate:

1. The map is 'wrong' - the convention is that 0,0 is bottom-left
2. The game tools are 'wrong' - there are additional, competing conventions that use top-left as 0,0, and said tools ought to cater for this eventuality
3. Neither are wrong - there are no firm conventions and though the many maps might tend towards 0,0=bottom-left, there are lots of other approaches commonly in use.

Note: A whole host of maps have A-Z+ as the x-axis and 0-n as the y-axis, with A1 being at the top-left, but I consider these as separate - these are intended to identify grids squares but not 6 and 8-figure coordinates.

I suspect the answer will be #3 but I will be interested to hear of any background/historical/supporting evidence.

Answer 1

The (0, 0) origin marks a placeholder coordinate system, that is designed to make use of standard distance, area and bearing calculations, but do not tie the image-space to a particular point on the planet. There is somewhat of a controversy over whether these maps can be called a "map" in the cartographic sense, or should only be referred to as plants (they are hardly ever used outside of construction blueprints). Regardless, this is not a discussion for now.

Cutting to the center of your question: the origin in an arbitrary coordinate system varies from field to field. There are actually two parameters at play:

• If the origin is at the lower-left or upper-left;

• If you reference the coordinates horizontal-vertical, or vertical-horizontal.

Different areas of human knowledge treat these differently. Mathematics treats cartesian planes with the origin in the lower-left (when dealing with positive numbers), and coords in horizontal-vertical (i.e., X and Y). Computer graphics, on the other hand, place the origin in the upper-left, and trace values horizontal-vertical, because of a legacy of how CRT monitors used to work (they'd begin drawing from the top row to the bottom). Matrices, on the other hand, have their origin in upper-left corner, but, read coordinates in the vertical-horizontal way.

The lack of a standard way to read tabular data can lead to confusion when changing fields, so it's important to first grasp exactly how a particular field or tool maps locations to a plane. In the specific case of videogames, the in-game coordinates are arbitrary and may be set to wherever the creator feels like it. It may be lower-left origin to mimick how plants are layed-out, or upper-left to map with the screen blit. Or anywhere else (I've seen games whose origin was at the centre, and objects would have positive and negative coordinates all over).

For a geographic map, however, one should stick to a a real-world coordinate system, which will map your origin to a specific place on Earth, regardless of your mapping area.