Currently, purple is not used in our revision program, but purple features are still present on many existing maps. At one time, purple was used as a revision color to show all feature changes.

The colors of the lines usually indicate similar classes of information: topographic contours (brown) lakes, streams, irrigation ditches, and other hydrographic features (blue) land grids and important roads (red) and other roads and trails, railroads, boundaries, and other cultural features (black). Many features are shown by lines that may be straight, curved, solid, dashed, dotted, or in any combination. The first features usually noticed on a topographic map are the area features, such as vegetation (green), water (blue), and densely built-up areas (gray or red). On some maps, post offices, churches, city halls, and other landmark buildings are shown within the tinted area. In densely built-up areas, most individual buildings are omitted and an area tint is shown. For larger buildings, the actual shapes are mapped. For example, individual houses may be shown as small black squares. Features are shown as points, lines, or areas, depending on their size and extent. Reading Topographic Maps Interpreting the colored lines, areas, and other symbols is the first step in using topographic maps. On one type of large-scale topographic map, called provisional, some symbols and lettering are handdrawn. Examples of symbols that have changed include built-up areas, roads, intermittent drainage, and some lettering styles. Consequently, within the same series, maps may have slightly different symbols for the same feature. These symbols are constantly refined to better relate to the features they represent, improve the appearance or readability of the map, or reduce production cost. The map includes symbols that represent such features as streets, buildings, streams, and vegetation. A topographic map shows more than contours. Contours make it possible to measure the height of mountains, depths of the ocean bottom, and steepness of slopes. Contours are imaginary lines that join points of equal elevation on the surface of the land above or below a reference surface, such as mean sea level. The distinctive characteristic of a topographic map is that the shape of the EarthвЂ™s surface is shown by contour lines. 'We recognize the fundamental role of government in acquiring mapping information and putting it in the public domain.ДЄt the same time, we recognize the tremendous benefits of the private industry adding value through innovative approaches to access and distribution.Topographic Map Symbols What is a Topographic Map? A map is a representation of the Earth, or part of it. 'We are so pleased to see these historic topographic maps being made more accessible to the nation,' said Kevin Gallagher, associate director ofД¬ore Science Systems for the USGS. Learn more about the image service in the item description in ArcGIS Online. The USGS Historical Topographic Maps image service thatД¬an be viewed on the web and provides links to allow users to download individual scanned images.

Using ArcGIS, the scanned maps were made into All maps were georeferenced, and metadata was captured as part of the The USGS scanned each map as is to capture the content and condition of each map sheet. Some scales have broad coverage across the United States, while others may have only one map. The collection includes all scales and allД®ditions of the topographic maps published by the USGS since the inception of the topographic mapping program in 1879. The historical maps are part of the USGS Historical Topographic Map Collection вЂ• a project that was launched in 2011. Learn more about the app in the item description on ArcGIS Online. The USGS Historical Topographic Map Explorer allows users to explore the historical maps, save the current view as a web map, and download the maps as high-resolution georeferenced images in GeoTIFF format for use in web mapping applications and GIS. Previously available only as printed lithographic copies, the legacy quadrangles are now available as web viewable images and free, downloadable digital files. This app brings to life more than 178,000 maps dating from 1882 to 2006. In 2014, the US Geological Survey (USGS) and Esri collaborated to bring the ever-increasing collection of US historical topographic maps to everyone through the USGS Historical Topographic Map Explorer. About the USGS Historical Topographic Map Collection and Explorer

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