Salt Lake County Aerial Photographic Maps

Collection

Identifier: PD-001

Staff Only

Scope and Contents

The 1946 aerial photographs are black and white original prints measuring 30” x 30” with a scale of one inch = 600 feet. They identify public streets, interstates, buildings, mountain ranges, and wetlands with the most detail. There are two indexes for the 1946 set. One is by location/general street range and the other is by federal index. The federal indexes are labeled 1 through 3 and fit together to form one large photograph of the county. Locate the desired grid on the appropriate index and note its federal ID number. Using the index in this binder, locate the federal ID number and note the corresponding drawer number for the map case. The photographs are located in the map case. The index in the binder is arranged by federal index number first then by federal ID number and gives the general geographical location contained in each image.

The 1952, 1958, and 1964 aerial photographs are on microfiche. There is a large grid map index for each year. Locate the desired grid on the index map then find the relevant year in the microfiche sections. Locate the correct grid number on the microfiche. Missing aerial photographs are noted. The 1979 aerial photographs are original prints. Some may have pencil and ink drawings on them that were used to plan future projects.

There are several missing photographs. The Archives does not have a complete set of aerial photographs for any of the above years.

Dates

1946-1979

Creator

Salt Lake County Planning and Development (Creator, Organization)

Conditions Governing Access

The collection is open for research.

Biographical / Historical

Farmers who participated in farm programs when they began in 1933 needed to have an accurate measurement made of their farms. However, precise measurement could only be made by surveyor’s chains being carried around the fields and maps then drawn by hand. A quicker, cheaper way had to be found since there were millions of acres to measure and map across the country. In 1935 the USDA began to use rectified-to-scale aerial photos to more efficiently measure acreage.

Vertical photography is used for rectified photographs. Actual overflying and photographing of land is done by private companies on a contractual basis. The camera is mounted so that it points straight down from the aircraft. Since the aircraft is constantly affected by wind currents, changing ground elevation, and the motion of the aircraft during flight, the camera is often at an angle off the true vertical. The resulting photo is tilted. This distortion must be compensated for in order to obtain rectified (accurate/true-to-scale) photographs. Correction is accomplished by a system of analytical aero triangulation which measures known points on a photo and mathematically computes scale and tilt data necessary for scale-accurate photos. This data is then used when making scaled enlargement on specialized rectifying enlargers and maintains an accuracy greater than 99% for most cropland. The final rectified aerial photograph is, in effect, a photographic map accurately representing ground features.

Today, aerial photographs cover all the nation’s major cropland areas and when properly delineated and annotated, serve as the basic record of owner operator units and land use utilization. Aerial photographs are valuable in many other ways besides crop measurement. They provide information in: conservation practices; urban development and planning; tax assessment; pollution studies; drainage programs; boundary determination; road location and highway development; pipeline and power line construction; watershed and reservoir planning; and the historical record of property changes.

Source: “How Aerial Photos Can Help You” brochure, U.S. Department of Agriculture, ASCS Aerial Photography Field Office, November 1992.