Abstract
This dataset consists of twelve aerial photographs acquired in 1937 by the U.S. Soil Conservation Service covering portions of the Altar Valley in southern Arizona. The photographs were produced at an approximate scale of 1:62,500 using Fairchild aerial survey technology and represent one of the earliest surviving systematic aerial photographic surveys of the region. The imagery provides a historical record of landscape conditions, transportation corridors, settlement patterns, vegetation, drainage networks, and land use during the late 1930s. The source photographs were georeferenced, trimmed, mosaicked, exported, and reprojected as a single-band 8-bit TIFF raster in NAD 1983 UTM Zone 12N to support historical, geographic, environmental, archaeological, and land-use research.
Purpose
The purpose of this dataset is to provide a historical aerial photographic baseline for the analysis of landscape change and historical geography in the Altar Valley of southern Arizona. The imagery supports the identification and interpretation of historical roads, trails, settlements, water features, vegetation patterns, drainage features, cultural features, and other landscape elements that may no longer be visible or may have been substantially altered. The dataset is intended for historical and interpretive research, spatial comparison, and general landscape analysis. It is not intended for engineering, surveying, legal boundary determination, or other applications requiring high positional accuracy.
Supplemental Information
The aerial photographs in this dataset were acquired in 1937 for the U.S. Soil Conservation Service using specialized Fairchild aerial mapping technology developed under the direction of Sherman M. Fairchild (1896-1971), founder of the Fairchild Aerial Camera Corporation. Fairchild was a pioneer in aerial photography and photogrammetry whose innovations transformed large-area mapping in the United States. Fairchild Aerial Camera Corporation was founded in 1920 to develop, manufacture, and sell aerial photographic equipment. Popular Mechanics reported in October 1935 that Fairchild equipment developed for the Federal Erosion Survey used ten synchronized cameras operating from altitudes of approximately 23,000 feet, enabling rapid photographic mapping over extensive areas. Fairchild also developed aircraft intended specifically for aerial survey work, addressing the stability and altitude limitations of many contemporary aircraft. Although these photographs are commonly attributed to the U.S. Soil Conservation Service, the imagery reflects the significant technological contributions of Sherman Fairchild and Fairchild Aerial Camera Corporation, whose cameras, aircraft, and survey methods helped make large-scale aerial mapping practical during the early twentieth century. References: Popular Mechanics, October 1935, Volume 64, Number 4, page 535, Wide Area is Mapped from Air by Giant Ten-Lens Camera; Smithsonian Institution, National Air and Space Museum Archives, Fairchild Industries, Inc. Collection, finding aid prepared by Kristine L. Kaske, 2003.
Spatial Extent
| West Bounding Coordinate | -111.75 |
|---|---|
| East Bounding Coordinate | -110.99 |
| North Bounding Coordinate | 32.25 |
| South Bounding Coordinate | 31.32 |
Bounding coordinates are expressed in geographic coordinates.
Raster Properties
| Format | TIFF / GeoTIFF raster mosaic |
|---|---|
| Rows | 41642 |
| Columns | 36088 |
| Number of Bands | 1 |
| Pixel Type | Unsigned char |
| Pixel Depth | 8 bit |
| Cell Size | 3.1108660610560372 meters by 3.110866061056038 meters |
| Compression | None |
| Pyramids | 6 levels, nearest-neighbor resampling |
| Uncompressed Size | 1.40 GB |
Spatial Reference
| Coordinate System | NAD 1983 UTM Zone 12N |
|---|---|
| Grid System | Universal Transverse Mercator |
| Horizontal Datum | North American Datum of 1983 |
| Ellipsoid | GRS 1980 |
| Semi-major Axis | 6378137.0 |
| Denominator of Flattening Ratio | 298.257222101 |
| Planar Distance Units | Meters |
Data Quality and Positional Accuracy
Positional accuracy was evaluated using twenty-two checkpoints located on terrain and cultural features visible in both the historical imagery and contemporary NAIP imagery accessed through Esri Online basemaps. Checkpoints included hilltops, road intersections, road curves, stock tanks, dams, washes, ponds, ridges, and other identifiable landscape features. Differences between checkpoint locations in the historical imagery and the reference imagery were calculated in the easting and northing directions. RMSE in easting was 33.3 meters and RMSE in northing was 36.7 meters, producing a radial RMSE of 49.6 meters. Estimated horizontal accuracy at the 95 percent confidence level is approximately 85.8 meters. Because many checkpoint features are difficult to identify precisely within the 1937 imagery, these statistics should be considered approximate and suitable only for general assessments of spatial alignment.
Lineage and Processing
Source
1937 Soil Conservation Service aerial photographs of the Altar Valley, Arizona
Processing Steps
- Acquired twelve scanned aerial photographs of the Altar Valley from Arizona State University Library collections.
- Identified latitude and longitude coordinates printed on the photograph corners. These coordinates correspond to U.S. Geological Survey 15-minute quadrangle boundaries.
- Georeferenced each photograph using the printed corner coordinates. The original coordinates were assumed to be referenced to the North American Datum of 1927 (NAD 27), consistent with the period and the associated USGS quadrangle framework.
- Trimmed the georeferenced photographs to remove white borders and non-photographic image margins.
- Merged the twelve georeferenced and trimmed photographs into a single raster mosaic covering the available 1937 Altar Valley imagery.
- Exported the mosaic and reprojected the dataset to NAD 1983 UTM Zone 12N.
- Assessed approximate horizontal positional accuracy using twenty-two checkpoints visible in both the historical mosaic and contemporary NAIP imagery. Calculated easting RMSE, northing RMSE, radial RMSE, and estimated 95 percent horizontal accuracy.
Keywords
- imageryBaseMapsEarthCover
- environment
- farming
- biota
- Fairchild
- Fairchild Aerial Camera Corporation
- Sherman M. Fairchild
- Soil Conservation Service
- SCS
- aerial photography
- historical imagery
- photogrammetry
- Altar Valley
- Arizona
- 1937
- NAIP
- georeferenced imagery
- mosaic
- landscape change
- historical geography
- United States
- Arizona
- Pima County
- Altar Valley
- southeastern Arizona
- southern Arizona
Access, Use, and Credits
Access Constraints
None
Use Constraints
This dataset is suitable for historical, interpretive, and general spatial analysis only. Positional accuracy is approximate and reflects the limitations of the 1937 source imagery, printed corner coordinates, georeferencing from historical map coordinates, and feature-identification uncertainty. The dataset must not be used for engineering, surveying, legal boundary determination, or any other purpose requiring high positional accuracy. Users should independently verify all information before relying on it for analysis or publication.
Credits and Rights Statement
Source photographs provided by Arizona State University Library collections. Historical aerial survey technology credited to Sherman M. Fairchild, Fairchild Aerial Camera Corporation, Fairchild Inc., and the U.S. Soil Conservation Service. Georeferencing, mosaicking, positional assessment, and derivative metadata prepared by Robert E. C. Davis. © 2026 Robert E. C. Davis. All rights reserved.
Metadata Reference
| Metadata Date | 20260605 |
|---|---|
| Metadata Standard | FGDC Content Standard for Digital Geospatial Metadata |
| Metadata Standard Version | FGDC-STD-001-1998 |