This layer is a composite image of a set of 164 spectacular, large format, sharp, black and white vertical aerial photographs partially overlapping images covering San Francisco north of a line approximately between Merced Lake and Candlestick Point. Resolution generally better than one meter and much higher with high contrast features, for example the paint striping on a basketball court. Relative heights frequently discernible based on shadow cast of objects and structures. Handwritten date on index map indicates photographs taken in August, 1938. Owned by the San Francisco Public Library. (Authorship almost certainly incorrectly spelled in handwriting on index sheet as Harrison-Rikker). He married Charlotte Seward in the mid-1920s; after divorcing, he married Esther Miriam Munson in 1936 Aerial Photographer Harrison Clay (Chesley) Ryker (1898-1981) was born in Oakdale, CA. . He served in the U.S. Army for several years in Germany with the post-World War I occupational forces, and partook of educational opportunities at the University of California, Berkeley. Expanding on his hobby in photography, Mr. Ryker teamed with various pilots beginning aerial photography services out of the Oakland Airport and throughout the West. Colleagues included Lage Wernstedt of the U.S. Forest Service. He also worked with the Fairchild Aerial Camera Company (including an aerial survey of Puerto Rico) and Clyde Sunderland of Pacific Aerial Surveys. As well, he took photographs of the devastating 1923 Berkeley Fire, archived in The Bancroft Library. By 1938 Mr. Ryker was listed in business as a map publisher (see Polk's Oakland 1938 Street and Avenue Guide) based at 1924 Franklin St., Oakland. At that time, he had at least one patent pending for a stereoscope used for aerial photograph interpretation. The historic map layers in the Google Earth Rumsey Map Collection have been selected by David Rumsey from his large collection of historical maps, as well as some from other collections with which he collaborates. All the maps contain rich information about the past and represent a sampling of time periods, scales, and cartographic art, resulting in visual history stories that only old maps can tell. Each map has been georeferenced by Rumsey, thus creating unique digital map images that allow the old maps to appear in their correct places on the modern globe. Some of the maps fit perfectly in their modern spaces, while othersgenerally earlier period mapsreveal interesting geographical misconceptions of their time. Cultural features on the maps can be compared to the modern satellite views using the slider bars to adjust transparency. The result is an exploration of time as well as space, a marriage of historic cartographic masterpieces with innovative contemporary software tools. This layer is presented in the WGS84 coordinate system for web display purposes. Downloadable data are provided in native coordinate system or projection.