How accurate are USGS topo maps?
Turns out, USGS topo maps use the National Map Accuracy Standards. This means that 90 percent of the horizontal points tested by field survey teams are accurate to within 40 feet. Vertical points, to within half a contour line, or five feet, based on standard 7.5 minute, 10-foot contour lines.
What is the national map accuracy standard?
The National Map Accuracy Standard (NMAS) provides insurance that maps conform to established accuracy specifications, thereby providing consistency and confidence in their use in geospatial applications. The following information from the USGS National Geospatial Program Standards Web sitegenerally describes the NMAS.
Why are map called 7.5 minute topographic?
7.5 minute maps are so called because each covers 7.5 minutes of latitude and 7.5 minutes of longitude on the earth’s surface. On the ground, this is approximately equal to eight miles (north and south) by six miles (east and west).
How accurate is USGS lidar data?
Light Detection and Ranging (lidar) is a technology used to create high-resolution models of ground elevation with a vertical accuracy of 10 centimeters (4 inches).
What are accuracy standards?
Accuracy is the degree of conformity with a standard or a measure of closeness to a true value. Accuracy relates to the quality of the result obtained when compared to the standard. The standard used to determine accuracy can be: • An exact value, such as the sum of the three angles of a plane triangle is 180 degrees.
What is the positional accuracy of the topo map at the 90% confidence level?
As applied to the USGS 7.5-minute quadrangle topographic map, the hori- zontal accuracy standard requires that the positions of 90 percent of all points tested must be accurate within 1/50th of an inch (0.05 centimeters) on the map.
What is the standard size of a USGS topographic map?
22 x 27 inches
The size of printed 1:24,000-scale topographic maps distributed by the USGS can vary slightly, but they are typically 22 x 27 inches (higher latitudes) or 23 x 27 inches (lower latitudes). Those measurements include the map collar (the white margin around the map and the wealth of information in it).
What is the difference between a 7.5 and 15 minute quadrangle?
From approximately 1947-1992, the USGS produced the 7.5 minute series, with each map covering an area one-quarter of the older 15-minute quad series, which it replaced. A 7.5 minute quadrangle map covers an area of 49 to 70 square miles (130 to 180 km2).