The view that is presented by the aerial photograph is from above and, as a result, objects do not look familiar.
The points selected on the photograph must be identifiable on the ground or map of the same area and should be spaced in such a manner that a line connecting them will pass through or nearly through the center of the photograph Figure Selection of points for scale determination.
Focal Length-Flight Altitude Method. When the marginal information of a photograph includes the focal length and the flight altitude, the scale of the photo is determined using the following formula Figure Computation of scale from terrain level. When the ground elevation is at sea level, H becomes zero, and the formula is as shown in Figure Basic computation of scale from sea level.
A map on which the area covered by each photo is outlined and numbered or indexed to correspond to the photo is called an index map. There are two methods of preparing index maps.
The four-corner method Figures and requires location on the map of the exact point corresponding to each corner of the photo.
If a recognizable object such as a house or road junction can be found exactly at one of the corners, this point may be used on the map as the corner of the photo. If recognizable objects cannot be found at the corners, then the edges of the photo should be outlined on the map by lining up two or more identifiable objects along each edge; the points where the edges intersect should be the exact corners of the photo.
If the photo is not a perfect vertical, the area outlined on the map will not be a perfect square or rectangle.
After the four sides are drawn on the map, the number of the photograph is written in the enclosed area for identification. This number should be placed in the same corner as it is on the photo.
Four-corner method selection of points. Plotting, using the four-corner method.
A geologist will generally use aerial photographs instead of a map if they are available. Large-scale photographs, , or larger, provide the most satisfactory results. Some topographic features, such as shallow ravines, rocky knobs, or sinkholes, are too. To change from topographic maps to aerial photos, simply click your viewing format in the "Base Map" window. The view will change from map to photo and remain fixed upon your location. Lots of topographic map users find that aerial photos instantly improve their navigation ability - photos have LOTS of information that is not shown on any map. It looks like you've lost connection to our server. Please check your internet connection or reload this page.
The template method is used when a large number of photos are to be indexed, and the exact area covered by each is not as important as approximate area and location.
In this case, a template cardboard pattern or guide is cut to fit the average area the photos cover on the index map. It is used to outline the individual area covered by each photo. To construct a template, find the average map dimensions covered by the photos to be indexed as follows.
Multiply the average length of the photos by the denominator of the average scale of the photos; multiply this by the scale of the map. Do the same for the width of the photos. This gives the average length and width of the area each photo covers on the map--or the size to which the template should be cut Figure To index the map, select the general area covered by the first photo and orient the photo to the map.
Place the template over the area on the map and adjust it until it covers the area as completely and accurately as possible. Draw lines around the edges of the template.The identification of features on aerial photographs depends upon a careful application of five factors of recognition.
No one factor will give a positive identification; it requires the use of all five. What different types of aerial photographs are available through the USGS? The aerial photographs date as far back as the 's for the United States and its territories. Availability of specific coverage, film type, and acquisition dates vary from agency to .
To change from topographic maps to aerial photos, simply click your viewing format in the "Base Map" window.
The view will change from map to photo and remain fixed upon your location.
Lots of topographic map users find that aerial photos instantly improve their navigation ability - photos have LOTS of information that is not shown on any map. LAB 1: TOPOGRAPHIC MAPS AND AERIAL PHOTOS Learning Objectives: Understand how to read and interpret topographic maps and aerial photos Start thinking critically about landforms and the processes that create them Learn to use aerial photographs to identify and interpret landforms.
LAB 7: INTERPRETING TOPOGRAPHIC MAPS AND AERIAL PHOTOS Stereoscopic Viewing of Paired Contour Maps and Aerial Photographs a. Using stereoscopes to look at paired contour maps Draw the approximate boundaries between the 4 or 5 volcanoes you can identify on the map. 3. Mt.
St. Oct 12, · Topographic maps are similar to physical maps, which show the physical features of an area. Although in topographic maps, differences in elevation and changes in landscape are shown with the help of contour lines and not colors.