Grid Gallery

Grid Gallery

A map might have three kinds of grids:

The lat/long graticule.
A projected coordinate system used to locate points, which does not have to be the actual projection of the map, such as:
- UTM. Printing this on the map allows easy computation of coordiinates in the field, even with the map partially folded.
- SPCS
- A national grid, like the UK OS, Irish.
The native projected grid of the projection. While the GIS program uses these for plotting and computations, it will only be shown on the map if it is also used to locate points.
- Lambert conformal conic. This is used to locate points in the SPCS projections.
- Transverse Mercator
- Mercator. I don't know of a case where this is shown, or used in computations.

There might also be grids in two different datums, in the case where a region has two datums in common use, or changed the datum recently and old data or maps are still present.

The spacing of the grid should have the same intervals in both the x and y directions. If the GIS program allows you to set different spacings, you should override the defaults and make them the same. This can lead to challenges with labeling, but you can find a solution that is better than differential spacing.

Appropriate grids on the map depends on the usage of the map:

For a map for presentation purposes, or printing in a scientitific journal, a single grid should be sufficient, and the cartographer must decide which to use; the lat/long graticule should be strongly considered. This map will only be viewed on a printed page, or online, and will have a restricted size, typically a few thousand pixels.
For a large paper map, one grid will probably be drawn, and the lat/long graticule might be indicated with internal ticks on the map and labels along the margins. If a second grid is required, it would have only ticks on the margin, and a user would have to connect them to measure coordinates in the field. This map could have the equivalent of tens of thousands of pixels in each dimension.

Three grids on a map of Rabat:

Lat/long graticule
UTM
Native Lambert conformal conic

This is probably impossible to use effectively, even with three different colors, but shows the possible changes, and how they differ.

Lat/long graticule for two datums

WGS84
Merchich Morocco

Note the datum shift is (almost) entirely in the east-west direction; the WGS 84 layer is plotted second, and the east west parallels completely overprint the secondary datum. There could a north south shift, but it is less than the pixel size on this map.

Lat-long graticule with lines

Graticule is not square, because a degree of latitude does not equal a degree of longitude.
You should be able to see that the "rectangles" are taller than they are wide.
If the graticule is "square", you are either at the equator or have a map with bad distortion.
You can set the graticule spacing.
If the graticule parallels the edges of the map, you have a geographic projection (like Mercator)
If the graticule does not parallel the edges of the map, you have a projection like UTM.

Lat-long ticks. Set spacing of the ticks.

Option on map toolbar or by right clicking on the map window.

Print button on map toolbar has Prepare printer image option that gives great control over a lat/long or UTM grid, or both.

Also from right click on the map, Copy to clipboard, Detailed map.

Last revised 11/25/2017