USGS 1:24000 Legacy Topographic Map (1942-2002)

Data Source

This map is hosted at boydsmaps.com

Description

The United States Geological Survey (USGS) began creating 24k topographic maps in the 1940's and completed the series in 1992 with revisions continuing through 2006. The "24k" name refers to the map scale of 1:24000 which means objects in the real world are 24,000 times larger than they appear on the map. In other words, one inch on the map equals 2,000 feet on the ground (24000/12 inches = 2000 feet).

These maps are also identified by their coverage of 7.5 minutes - one degree consists of 60 minutes, so this is equivalent to 1/8 of a degree. Starting in 2009, the USGS began replacing these legacy maps with their new digital "US Topo" series which unfortunately does not contain the same amount of detail. In discontinuing the legacy maps, the USGS explained:

"Traditional national mapping programs gathered data from primary sources, including direct field observation. Such maps were compiled, drawn, and edited by hand. In the United States, the era of traditional topographic mapping lasted from about 1880 to about 1990, and was primarily the responsibility of the U.S. Geological Survey (USGS). By today's standards these traditional methods were very expensive, and USGS no longer has either mission or funding to make maps this way."

This map (available exclusively at boydsmaps.com) is a curated collection of 7,438 24k topographic quadrangles from the USGS Historical Topographic Map Collection, newly downloaded and stitched together (about 13 million map tiles).

The map includes full coverage of Connecticut, Delaware, Maine, Maryland, Massachussets, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, Vermont, Virginia and West Virginia with partial coverage of Indiana, Kentucky and Michigan. This is an ongoing project and coverage will be expanded to a larger area in the future.

Original .tif files were downloaded from the Historical Topographic Map Collection, cropped to remove the collar and re-projected as Web Mercator (EPSG: 3857). These source files were processed at a resolution of 2.4 meters/pixel (zoom level 16) which preserves the full detail of the original USGS 300 dot-per-inch scans.

The 24k maps are shown at zoom levels 14, 15 and 16. Zoom level 13 is a mosaic of 275 USGS 100k topo maps and zoom levels 10, 11 and 12 consist of 88 USGS 250k topo maps. Zoom levels 5 thru 9 show the USGS National Map Topo Basemap. Note that just about all of the 100k maps use the metric system of measurement, a possible source of confusion when looking at elevations.

In most cases the newest version of each 24k quadrangle was chosen, but older versions were sometimes used if there were quality issues. The following table shows the number of maps that were used from each decade, however the dates reflect the year in which the map was originally created and not necessarily the most recent revision. In some cases, no suitable historical topo map was available and digital maps from the US Topo series were used. These are reflected in the numbers from the period 2010 through 2022.

Apparently, most of the Adirondack Mountains in New York were never mapped at 1:24000 scale (see below). Instead, these areas were mapped at 1:25000 scale in the 1980's and 1990's, with maps that cover twice the area of the 24k topos (7.5 minutes x 15 minutes). These maps are slightly lower resoltion, although it is not especially noticeable. But these maps were created using the metric system and the elevation contours are labelled in meters, which is very confusing. In these areas, note that the elevation display in the top left corner of the map will show the correct elevation in feet (if you are using the default imperial units). Parts of Michigan have also been mapped at 1:25000 scale with the metric system.

Resources

See the following document for information about the symbols that are used on USGS topographic maps:

A document explaining topographic map scales is available here:

Credits

Original maps from the US Geological Survey Historical Topographic Map Collection and National Map Topo Basemap.

www.usgs.gov/core-science-systems/ngp/topo-maps/

basemap.nationalmap.gov/arcgis/rest/services/USGSTopo

Distribution Liability

Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the accuracy or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. This disclaimer applies both to individual use of the data and aggregate use with other data. It is strongly recommended that these data are directly acquired from a U.S. Geological Survey server, and not indirectly through other sources which may have changed the data in some way. It is also strongly recommended that careful attention be paid to the contents of the metadata file associated with these data. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and/or contained herein.

The digital version of the historical map was georeferenced with a methodology that preserves, but does not exceed, the accuracy of the original map. The historical map product was compiled to meet National Map Accuracy Standards (NMAS) of the era when the map was originally published. Users should be aware that temporal changes may have occurred since this map was originally produced and that some parts of this data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations.

Map software is provided "as is", without any express or implied warranty. In no event will boydsmaps.com be held liable for any damages arising from the use of this software. The user assumes all risks associated with the use of this software. boydsmaps.com will not be held responsible for any inaccuracies and no responsibility is assumed for damages or other liabilities due to errors, installation, accuracy, availability, use or misuse of the data presented.