Data Sources & Accuracy for NPS Maps

Section of Zion National Park map, Utah.

National Park Service maps are graphical products designed for general reference, orientation, and route finding. Do NOT use these maps for backcountry hiking, navigation, GPS referencing, mountaineering, and other specialized activities—use US Geological Survey (USGS) topographic maps instead. National Park Service maps do NOT have legal authority. They are NOT official boundary documents, and, because of their small scale and generalized nature, do not necessarily show small outlying park areas and private inholdings.

Most of the digital maps at this site derive from traditionally produced maps revised and printed during the past 20 years. An increasing number of more recent maps, however, derive from Geographic Information System (GIS) and USGS Digital Line Graph (DLG) sources.

Because of graphical modifications, it is not appropriate to import the maps on this site into GIS applications.

RELATED LINKS:

National Mapping Program Standards »

U.S. Board on Geographic Names »

USGS Digital Line Graph (DLG) sources »

Example of NPS park map linework.

Linework

The linework on National Park Service maps originates from USGS sources that meet National Mapping Program Standards. However, manual production processes prior to map digitization often diminishes the accuracy of the original data. Factors contributing to inaccuracies include the stretch and shrinkage of USGS paper maps, camera lens distortion when photographing a composite base map, and manual drafting of lines.

The National Park Service uses stringent map digitizing standards to minimize the introduction of additional errors when digitizing traditional maps. For example, the size difference between digitized maps and the traditional bases from which they derive never varies more than 0.005 inch across the full extent of the map. The map digitization standards also preserve the visual character of features. For example, sinuous line strings comprised of tight Bezier curves depict streams and graceful Bezier arcs represent major roads.

Linework on the more recent maps derive from GIS and USGS DLG sources, albeit in a modified form. Typical modifications to linework (and other vector data) include removal of excess and/or inaccurate anchor points, conversion of linework to bezier curves, and slightly changing the position of lines in congested areas to improve legibility.

Be aware that linework running off the printed area of maps is sometimes fictitious and serves only as bleed for cropping. Some classes of map data, especially hiking trails, derive from non-surveyed or field-checked sources.

Example of NPS park map shaded relief.

Shaded Relief

Shaded relief is the graphical portrayal of topography in a natural manner using modulated light and shadows. Shaded relief on most National Park Service maps derives from manual techniques using airbrush, pencil, and paints applied to stable base materials. More recent shaded relief, however, derives from digital production.

The registration of scanned shaded relief art to drainages and other map linework occurs in Adobe Photoshop. In the event of registration discrepancies, the NPS modifies the shaded relief—using the standard array of scaling, distortion, and paint tools in Photoshop—to ensure a close fit with the linework. We never alter or reposition linework to fit shaded relief.

The resolution of shaded relief at final size is generally 200 dpi, intended for printing with 175 lpi screens. Our testing has shown that higher resolution adds no additional relief detail, but only increases files to unwieldy sizes.

Examples of NPS park map cartographic symbols.

Point Symbols

Locator dots show the general location of points of interest. The position of dots for sites covering large areas, such as campgrounds and picnic areas, are approximate. To enhance legibility, features represented by point symbols on the map are exaggerated in size compared to their true size at map scale.

Elevation dots come from USGS sources. To register summit elevation dots with shaded relief bases, we sometimes adjust the position of the dots slightly.

Examples of NPS park map scales, milage indicators, and point elevations.

Numbers and Scale

Elevations in feet come from USGS maps, from which we calculate the metric elevations rounded to the nearest whole number.

Mileage distances derive from odometer readings rounded to the nearest whole number, as are equivalent distances in kilometers.

Because National Park Service maps must fill the available space on a brochure, they seldom match the scales of standard USGS map series. To calculate a numerical scale, use the bar scale found on almost every map.

Place Names

Geographic feature names derive from USGS maps and conform to U.S. Board on Geographic Names standards, although discrepancies may exist. Check with the Board to confirm all spellings.

Other naming discrepancies may exist for categories of features not covered by the Board such as the names of trails, roads, park facilities, and points of interest. Name changes to these features are not uncommon; National Park Service maps generally show the most recent names endorsed by park officials.

National Park Service maps use diacritical marks for spelling Hawaiian place names where approved by the Board on Geographic Names.

Note: The National Park Service uses a proprietary font for labeling Hawaiian maps that is not released publicly. Due to font substitution, diacritical marks do not appear on downloaded maps. Check printed National Park Service maps for the correct spelling of all Hawaiian place names.