A topographic map may be obsolete because it was compiled many years ago. A recent aerial photograph shows any changes that have taken place since the map was made. For this reason, maps and aerial photographs complement each other. More information can be gained by using the two together than by using either alone.
a. Advantages. An aerial photograph has the following advantages over a map:
(1) It provides a current pictorial view of the ground that no map can equal.
(2) It is more readily obtained. The photograph may be in the hands of the user within a few hours after it is taken; a map may take months to prepare.
(3) It may be made for places that are inaccessible to ground soldiers.
(4) It shows military features that do not appear on maps.
(5) It can provide a day-to-day comparison of selected areas, permitting evaluations to be made of enemy activity.
(6) It provides a permanent and objective record of the day-to-day changes with the area.
b. Disadvantages. The aerial photograph has the following disadvantages as compared to a map:
(1) Ground features are difficult to identify or interpret without symbols and are often obscured by other ground detail as, for example, buildings in wooded areas.
(2) Position location and scale are only approximate.
(3) Detailed variations in the terrain features are not readily apparent without overlapping photography and a stereoscopic viewing instrument.
(4) Because of a lack of contrasting colors and tone, a photograph is difficult to use in poor light.
(5) It lacks marginal data.
(6) It requires more training to interpret than a map.