Contour maps give essential information about the relief of an area. Aerial photographs provide a quick means for preparing valuable sketches and overlays for your field party. Direct aerial observation gives you an overview of an area that speeds up later ground reconnaissance if the region has already been mapped. Begin the study of a map by marking the limits of the area to be reconnoitered and the specified terminals to be connected by the highway. Note whether or not there are any existing routes. Note ridgelines, water courses, mountain gaps, and similar control features.

Look for terrain that will permit moderate grades without too much excavating. Use simplicity in alignment and have a good balance of cuts and fills; or use a profile arrangement that makes it possible to fill depressions with the cut taken from nearby high places. Mark the routes that seem to fit the needs and that should be reconnoitered in the field. From the map study, determine grades, estimate the amount of clearing required, and locate routes that will keep excavation to a minimum by taking advantage of terrain conditions. Mark stream crossings and marshy areas as possible locations for fords, bridges, or culverts.

Have the reconnaissance field party follow the route or routes marked earlier during the map study. Field reconnaissance provides you with an opportunity for checking the actual conditions on the ground and for noting any discrepancies in the maps or aerial photographs. Make notes of soil conditions, availability of construction materials, such as sand or gravel, unusual grade or alignment problems, and requirements for clearing and grubbing. Take photographs or make sketches of reference points, control points, structure sites, terrain obstacles, landslides, washouts, or any other unusual circumstances.

Your reconnaissance survey party will usually carry lightweight instruments that are not precise. Determine by compass the direction and angles. Determine the approximate elevations by an aneroid barometer or altimeter. Use an Abney hand level (clinometer) to estimate elevations and to project level lines. Other useful items to carry are pocket tapes, binoculars, pedometer and pace tallies, cameras, watches, maps, and field notebooks.

Keep design considerations in mind while running a reconnaissance survey. Remember that future operations may require further expansion of the route system presently being designed. Locate portions of the new route, whenever possible, along roads or trails that already exist. Locate them on stable, easily drained, high-bearing-strength soils. Avoid swamps, marshes, low-bearing-strength soils, sharp curves, and routes requiring large amounts of earthmoving. Keep the need for bridges and drainage structures to a minimum. When the tactical situation permits, locate roads in forward combat zones where they can be concealed and protected from enemy fire. The report you turn in for the reconnaissance field party must be as complete as possible; it provides the major data that makes the selection of the most feasible route or routes possible.

PRELIMINARY SURVEY. A preliminary survey is a more detailed study of one or more routes tentatively selected on the basis of a reconnaissance survey report. It consists essentially of surveying and mapping a strip of land along the center line of tentatively selected route.

Some of the activities associated with preliminary survey are as follows: running a traverse (sometimes called a P-line or survey base line), establishing BMs, running profiles, and taking cross sections. For many projects, the preliminary survey may be conducted by a transit-tape party alone. Other projects may require a level party and a topographic party.

Normally, the data gathered from a preliminary survey are plotted while the party is in the field, This practice gives a more accurate representation of the terrain, reduces the possibility of error, and helps to resolve any doubtful situations while you are actually observing the terrain.