The neatline is not a perfect rectangle on any standard quadrangle projection used by the USGS, but for small areas it is nearly rectangular. The quadrangle is oriented on the paper so that the boundaries of the neatline are approximately parallel to the edges of the paper. A plane coordinate grid is oriented to the projection's central meridian. At the physical file level, a DRG is a simple raster image. Each cell in the array is exactly one pixel.
All pixels are the same size.
The data set is perfectly rectangular and perfectly planar. A DRG therefore has the geometric characteristics of a projected plane grid, not those of a graticule. For this reason, it is useful to align the rows and columns of a DRG with the rows and columns of a plane ground coordinate system. This makes the relationship between image coordinates and ground coordinates arithmetically simple. Figure 7 shows the boundaries of digital data sets associated with a Transverse Mercator map.