How to... Produce UTM Grid maps
Areas contained within a single UTM longitude Zone
This is very straightforward. All that is needed is a Boundary (BDY) file containing the UTM Grid co-ordinates of the map to be plotted. See the topic Grid Reference BDY files for information about obtaining such a file, including a useful downloadable utility program for converting a latitude+longitude BDY file to a single zone UTM Grid Reference BDY file. Once the map is set up within DMAP, the UTM Grid lines can be superimposed on the map simply by setting the required grid spacing in Options|Map Parameters, and the symbol sizes can be specified in Km.
Areas covering more than one UTM zone
The complication here is that each UTM Zone has a separate projection and the projected grid lines of adjacent Zones should be plotted at an appropriate angle to each other when plotted on a projection 'common' to all Zones. The base map therefore has to be in units of the projection 'common' to all Zones rather than in units of any of the constituent Zones. The easiest way to achieve this is to use latitude+longitude as the 'common' projection; the base map being a latitude+longitude Boundary file. See the topic Latitude+Longitude BDY files for information about obtaining such a file. The grid automatically overlaid on this map by DMAP will be in latitude+longitude units. UTM Grid References which are placed in the Distribution Data file will be automatically converted to their correct positions on the latitude+longitude base map. The Iberian Peninsula example map supplied in the DMAP package is an example of this approach.
Setting appropriate symbol sizes
Symbol sizes are set in DMAP at the Options | Map Parameters dialogue box. On a latitude+longitude base map, the units for symbol size are minutes rather than Km. The following procedure can be used to set an appropriate symbol size for UTM Grid Reference data plotted on a latitude+longitude base map:
- Calculate the N-S Symbol Size as the required size in Km multiplied by 0.54. For example, if you are plotting 10Km UTM Grid References, the size in minutes would be 5.4. Enter this value for the N-S Recording Unit and Symbol Size Parameters.
- Calculate the E-W Symbol Size by multiplying the N-S Symbol Size by the Aspect Ratio of the map. For example, with a N-S Symbol Size of 0.54 and an Aspect Ratio of 1.60, the E-W Symbol Size would be 8.6. Enter this value for the E-W Recording Unit and Symbol Size Parameters.
- If you require smaller (or larger) symbols, you can adjust the values of the Symbol Size Parameters, although you should maintain the correct aspect ratio between the E-W and N-S size. You should, however, leave the Recording Unit Parameter values as calculated in steps 1 and 2 above, so that the symbols remain correctly centred in their grid squares.
Superimposing UTM Grid lines
A UTM Grid can be superimposed on the latitude+longitude base map, but it requires some additional work. Each separate line which comprises the UTM Grid must be added to a latitude+longitude BDY file. Each line should be specified as the UTM Grid Reference of one end of the line, followed by the UTM Grid Reference of the other end of the line, followed by
For example (a north-south UTM 10km grid line across Spain):
30TVP52 30SVF56 -1
DMAP will convert these Grid References to latitude+longitude co-ordinates and then plot a line between these points. By inserting pairs of Grid References for all the lines making up the required grid, it is possible to create the grids for any UTM Zones covered within the area of the map. The overlaid latitude+longitude grid should then be switched off at Options|Map Style.
For maps covering large areas, where the UTM Grid lines may be slightly curved rather than straight, it may be necessary to specify some intermediate points along each grid line rather than just the two end points.
NEW! A utility program (GridGen) is now available which can automatically generate BDY files containing UTM Grid lines. See the Add-on Utilities page.
For more information about UTM Grid References, see:
If you have any comments, suggestions or queries about this procedure, Contact Alan Morton