How to read a Sanborn fire insurance map (and find your street on one)

What they are The Sanborn Map Company drew detailed maps of American towns from 1867 through much of the twentieth century, so that fire insurers could judge risk building by building. For many towns they are the most detailed record of what stood on each lot, and when. Where to find them - The Library of Congress has digitised a large part of its Sanborn collection, free and in high resolution: https://www.loc.gov/collections/sanborn-maps/ - Many state universities host their own state's sheets. In Texas, check the University of Texas libraries. How to read one - Each volume opens with a key map and a street index. Find your street there and it gives you the sheet number. - Colour shows construction: pink is brick, yellow is frame (wood), blue is stone, and grey is iron or other fireproof construction. - Numbers inside a building give its height in storeys. Letters mark use: D for dwelling, S for store, F for flat. - Small notes record the roof material, chimneys, the location of the water main, and the fire hydrants. - Lot lines and house numbers are shown, though house numbers were often changed later. Using them to date a building Compare editions. If a lot is empty in one edition and shows a frame dwelling in the next, the house went up in between. Many towns were updated with paste-over corrections, so check the date on the sheet as well as the volume. Post here The town, the edition year, the sheet number, and what changed between editions.