|The World Map Project (Peace Corps)|
These instructions are for mapmakers who are drawing their maps on unsquared walls or irregular pieces of hanging canvas. Don't be put off by the number of steps. They simply tell you how to make a grid box with perpendicular sides using a simple plumb line.
simple plumb line
Attach a long string to a small flat weight, such as a washer or rock. The string should be longer than the height of your map. The weight should be about the size and shape of a half-dollar. It should also be smooth and flat on one side.
1. Roughly center your map on your background surface. You can find the center point of your map by drawing a big X corner-to-corner across an area of background that is roughly the same size as your map. The center of the X is the center point of your map's grid.
2. Draw the left edge of your grid box:
a. From your center point, measure left 1/2 the length of your map. Let this be Point L.
b. Hang your plumb line through Point L. Tape the top of the string to the wall so that the plumb line crosses directly over Point L. Your plumb line should lie directly against the wall or cloth. When it is still, make marks on the background surface every foot (half-meter) or so down along the string.
c. Connect these marks with a pencil and straightedge to make the left edge of your grid.
3. Draw the bottom of your grid box:
a. Decide where you want the bottom of your map to be. Measure up from the floor this distance and make a series of marks the length of your map.
b. Connect these marks with a pencil and straightedge to make your bottom line.
Figure 10: Grid Box Left Edge and Bottom Line
4. Draw the right edge of your grid box. Repeat steps 2a-c on the right side of your map. (Let R be the right edge point and B be the point of intersection between the bottom line and the right edge line.)
5. Draw the top of your grid box:
a. Mark the height of your map on both the left and right sides of your grid box. Do this by measuring up from Points A and B the same distance. Let the top left point be Point C and the top right point be Point D.
b. Draw a line connecting these two top marks (Points C and D). This top line should be parallel with the bottom line. If you don't have a very long straightedge, first make top points.
Figure 11: Grid Box Right Edge and Top Line
6. Now that you have your grid box, (go to Make sure your box is squared or go to Draw your grid lines) and continue the process from there.