The Map Table

I feel the best way to learn map reading is to build a map table. Read all of this before making one. You might think of other solutions. Surveyors used to make maps with a "plane table". We are using a map table and existing map to find landmarks that exist already on the map.

You need a level portable surface on a tripod to lay your maps out flat. You need a way to attach or hold the map or map book down to the map board. You need to be able to turn and lock the map board to orient the map to point true north, usually at the top of the map. A center post tripod without a head or tripod and a pan head will do this

Good quality 3/8" or 1/2" plywood is fine for a map board. Find a builder's supply stores with cut pieces so you don't have to buy a whole sheet. I suggest one 9" x 12" for a Thomas Brothers Map Book, a 12"or 16" x 16" for a De Lorme Map Book and single sheet maps. Regular and large clip boards will also work, but will warp a bit.

Map table on Benbo tripod

Map table on Bogan tripod

These boards needs an ADAPTER to attach to your tripod.

Adapter Method #1: (You need drills. Some one with a wood shop would be a lot of help.) For 3/8"-16 threads, countersink a 1-1/8" hole about 3/16 deep with a wood paddle bit in a piece of 4" x 4" x 3/4" plywood. Drill all the way through with a 1/2" drill. (Put scrap wood on back side to prevent damage on back side.) Pull a 3/8"-16 TEE nut into the hole with a bolt and washer from other side. For 1/4"-20 threads use a 7/8" paddle bit, drill through with a 9/32" or 19/64" drill and attach 1/4"-20 "tee nuts" available from hardware stores. (You can use a 1/4" drill if you file it a bit larger.) The 1/4" tee nut will attach to a small tripod head and a 3/8" to a large head or center post of a small center post tripod. I suggest that you make a few of these as they are helpful to attach other things to your tripod or give to friends.

Tee Nut Here Plywood Adapter Shoe on Plywood

Adapter Method #2: If your tripod has a quick release attachment, buy a spare camera shoe. Drill holes in the quick release shoe and screw it to your map board or the 3" x 3" plywood adapter. Or screw the adapter to the 1/4" tee nut in the map board. If you are a mechanic you might figure other ways to make an adapter. (Send me your ideas.)

Clear Plastic Map Table on Tripod Adapter

Adapter Method #3. Attach the top of a 400' 16 or 35 mm metal film can with hot glue or double stick tape to your clip board or map board. Drill a 1/4" or 3/8" hole in the center of the bottom of the film can. Put the bottom of the can over the camera bolt on the tripod head or the top of the center post of the tripod. Tighten a 1/4" or 3/8" nut to hold the bottom of the can on the tripod. The can allows you to orient your map. If attached to a tripod head the tripod AND head must be level.

Film Can Adapter on Bogan Tripod

From a stationary store get some large paper spring clips or small hardware spring clips to hold the map or map book to your map table. You might also check out their 360 degree protractors, plastic rulers, and drafting tape while there.

Also needed:

1. A small roll of drafting tape and the spring clips to hold map to table.

2. A small torpedo level, bulls eye level, marble or angle finder to level the table. The angle finder is useful for other measurements. (Remove the magnets if it has them.) The angle finder can be used as a cheap clinometer.

3. Parallel Rules. (See Sun and Map Instrument Suppliers)

4. A 24 inch ruler or straight edge for making grid lines on topo maps.

5. A course plotter or 2 or 3 arm protractor.

USGS Topo Map Preparation. Find the longitude marks on the top and bottom of the map. They will be 1/3 in from the edges and be labeled XX' 30" or XX' Draw two vertical grid lines on the map joining these marks. These will help you find true north at your location with your parallel rules. With a map book join 2 or more maps together if necessary to cover the area you can see. Most map books have grid lines for orienting the map to north.

Drawing Grid Lines on Topo Map

For both styles of map tables find your exact location on the map. Make an X on that spot. Clamp the map with the areas you can't see near an edge of the table so that you can see areas with visible landmarks. Draw a vertical north/south line through your position with the parallel rules using the map edge or N/S grid lines you drew on the map.

Parallel Rules and Map

Place the center of course plotter/one or three arm protractor on your position and aligned with the north/south 0/360 vertical line through your position. Tape the protractor base to the map with drafting tape. The swinging arms of the plotter can now point to azimuths/directions of land marks on your map.

Course Plotter and Map

Once you have built your map table, take your map table and a good large scale map of a location where you can see a lot of landmarks that you can also find on your map. In Los Angeles, Mulhulland Drive 1/2 mile west of Cahuenga has a good wide spot for the Hollywood 7-1/2 Minute Hollywood Topo. Griffith Observatory is also good. From both places you can see Down Town L.A. and other identifiable landmarks. On Mt. Washington on Ave 43 you can also see down town and many identifiable points. It is important that you accurately locate your self on the map. Position the map on your table so that the visible landmarks are over part of the table.

Level the table or if the tripod has a center post make it vertical with a torpedo level. Now find a landmark that you can see and can find on the map. Line up an arm of the protractor with the landmark on the map and pan the tripod and map table until the landmark on the map and location line up. Lock the pan of the tripod or tape the film can together and see if other landmarks line up. If they do, you have accurately found your own location on the map and the map is oriented to the true north and real world.

Now look at your computer read out for sun position for the day and time and see if the sun is in the right azimuth/direction/bearing. You can now predict the sun's azimuth all day from sunrise to sunset. Notice that you didn't need your compass. Now check to see if your compass agrees with your map table directions. Remember the difference between magnetic and true directions. Your tripod may have magnetic parts that can effect your magnetic compass directions. Your car, eyeglasses, light meter, or motorcycle chain belt can also effect your magnetic compass. Sight on the landmarks as you did for aligning your map table.

© Copyright 1999-2004 Ron Dexter. All Rights Reserved.