As I have noted, I will be competing in this year’s Lejog rally in the United Kingdom. I was asked about the plotting of the route that must be done for this rally. With this post I hope to explain an approach to plotting the route on the maps. In order to explain the plotting techniques, first of all I want to show the map coordinate system used in the United Kingdom.
The coordinates used are based on the 1:50,000 scale Landranger Maps that I have referred to in the past. These maps use a coordinate system based on a northing and an easting with a 1 kilometer grid system. This coordinate grid is shown on every Landranger Map. This grid can be seen as blue lines on the image below of a portion of Landranger Map 187. Each of those blue squares measures 1 kilometer by 1 kilometer on the ground.
Blue Grid On The Landranger Maps Identifies The Northings And Eastings
On the above image the northing grid is illustrated by the faint blue horizontal lines that say 39, 40, 41, and 42 in this case. The numbers increase the farther north that the grid goes. The easting grid is illustrated by the faint blue vertical lines that say 08, 09, 10, 11, 12, and 13 in this case. The larger numbers are more easterly than the smaller easterly numbers.
The coordinates of points to be plotted as provided by the rallymaster can either be provided in a six digit style or the 8 digit style. Note that the northing is always the first number listed and the easting is the second number listed.
420 1/2 101
In the above example the northing is 420 1/2 while the easting is 101.
With the eight digit style, the northing is 4205 and the easting is 1010.
These two styles of point presentation represent the same point on the map. These points have a northing that is located 50 metres north of the 42 north grid line and an easting of 100 meters east of the 10 east of the 10 east grid line.
Now that the grid reference on the map is understood, a “romer” or “roamer” is needed to assist in the plotting of points on the map. I have seem the spelling both ways, but I think that “roamer” is more correct. And that is the spelling that I will use. I have a couple of roamers, but the one that I am planning on using for LeJog is shown below. It is shown on a white background for clarity, but my roamer is transparent.
My Roamer Used For Plotting Points And Measuring On A 1:50,000 Map
The upper right hand corner of the roamer is the key display that can be used to plot the locations on the Landranger Map. This display represents 1 square kilometer at a scale of 1:50,000 with increments as fine as 50 meters. This corner scale is more clearly shown in the image below. This 1 kilometer scale matches the grid squares on the Landranger Map.
The Upper Right Corner Is Used To Plot The Reference Points
The use of a roamer for plotting the route can be illustrated with the following example. This example uses Landranger Map 187. For this example, I will use the eight-digit style of presenting the coordinates. Assume for this example that the starting point has the coordinates of 4035 1110 and the next or end point of this simple route has coordinates of 4245 0995. A more complete description of a reference point will also include the Landranger Map number, such that the complete reference point description of the starting point for this example would be 187/ 4035 1110.
The image below shows how the starting point 4035 1110 is plotted using the upper right corner display of the roamer. Note that the vertical or northing scale is placed at 350 meters north or above the 40 northing grid line. Also note that the horizontal scale is placed at 100 meters east or to the right of the 11 easting grid line. The confluence of these two points is located at the very top right corner of the roamer.
Using The Roamer To Plot Coordinates On The Map
Once the two points, the starting and ending points of the example are plotted, the route to be followed is the shortest route between those two points. The image below shows the route to be followed marked in pencil on the map for the example that I have used.
Plotted Route Between Two Points On The Map
Once the route is plotted then the “poti” can be used to help follow the route.
If you have any questions or comments about this post or plotting a route on a map then leave a comment below or you can send me a private email message at the following address: shanna12 at comcast dot net