Class IV elevation data, equivalent to 1-foot contour accuracy, approximates
Quality Level 2 (QL2) from the National Enhanced Elevation
Assessment (NEEA) when using airborne lidar point density
of 2 points per square meter, and Class IV also serves as the basis for
USGS’ 3D Elevation Program (3DEP). The NEEA’s Quality Level 1
(QL1) has the same vertical accuracy as QL2 but with point density
of 8 points per square meter. QL2 lidar specifications are found in
the USGS Lidar Base Specification, Version 1.1.