A number of additional fire-relevant details are also provided on the maps, as understanding fire risk and fire fighting capabilities was their primary purpose. Note the water pipes and their diameters shown on the portion of a map shown below. The black circle with a D.H. above it indicates a double fire hydrant. Toward the bottom is a symbol with the letters F.E. next to it, indicating a fire escape. More detailed information was provided for industrial facilities and fire stations.
In the portion of map shown, the Great Northern Glove Manufacturing Company occupies the second floor of the structure. If you look closely, you'll notice that it includes the information that the facility is heated by stove and that power and lights are provided by electricity.
This wasn't always the case. Some small factories and machine shops in the early 20th century relied upon gasoline engines to power equipment. In some cases you'll find this noted, including the size of the gas tank(s) in use - but not on this particular bit of map.
|From the 1919 Sanborn map of Bluffton, Indiana|
The colors of the building as depicted on the map are also important. They help denote the construction of the building. The Library of Congress has a nice scan of one such key available. Short version: yellow is frame (wood) construction, pink is brick construction, blue is stone or concrete, and gray is metal - although a shade of gray is also used for adobe. There are various combinations that indicated combinations of materials, and abbreviations that modify, so a careful look at the key is called for.
So how can you look at these maps? Digital copies of the maps for a state are usually available free online from a state library and/or university. What's the catch? Oftentimes you can only access them from within that state, or with institutional credentials (library or university) from that state. Partially this is due to copyright. The ones from 1923 or later are still under copyright, but the ones from 1922 and earlier are in the public domain and may be made freely accessible. Partially this is due to budget reasons: its costs money to host and stream the maps.
Indiana University and Penn State University have their respective states' pre-1923 Sanborn maps freely available online, but later ones are only available to in-state users. They're in color. The Sanborn maps for Ohio are freely available to Ohioans, but not out-of-state - and they're only in black and white. New Jersey, Illinois, and Iowa seem to be in a similar situation to Ohio, but in color.
The Library of Congress has their digital collection of Sanborn maps accessible to all - but only a tiny fraction of their physical Sanborn map holdings have been digitized. For example, for New Jersey, only about a dozen cities and towns whose name start with "B" are available digitally - the rest of the alphabet need not apply. For Iowa, a small portion of the cities and towns whose names begin with "D" or "E" are available digitally. For some states, no digital Sanborn maps are available from the Library of Congress.
There's also a complete digital collection maintained by ProQuest. Alas, many institutions don't purchase access. Invidual access is pricey.
Despite some difficulty gaining full access to the maps, they can be quite useful for learning about the past of towns and cities of America. Data derived from the maps can be useful in many contexts. It can answer questions about urban growth, patterns of development, mix of stores, and other social, geographic and historic matters.
Alas, as I mentioned above, one are of personal interest where they've proven to be of little help is with respect to streetcars and electric interurban railways. Mostly, the map makers omitted them, unless they were conversions of steam railroads, or also used steam locomotives regularly. If they included them otherwise, it appears to have been by lucky coincidence. Stations and other facilities are generally shown, but the tracks themselves are not.
So, to conclude, the digital Sanborn maps offer a useful glimpse into the past. You can probably obtain easy access to your state's collection. Obtaining free access to those for other states may be trickier, but you may be lucky.