There are two common types of coordinate reference systems (CRS) used in engineering:
- A geographical coordinate reference system uses latitude–longitude coordinates to map the earth’s spherical surface. More information on geographic coordinate reference systems is provided here.
- A projected coordinate reference system uses X-Y coordinates (commonly called Northing and Easting) to project maps of the earth’s spherical surface onto a two-dimensional Cartesian coordinate plane. More information on projected coordinate reference systems is provided here.
Since HEC‑RAS utilizes X-Y coordinates for defining elements of the river system, only projected coordinate reference systems can be used. However, GeoHECRAS will automatically reproject data sets that use geographical coordinate reference systems to the assigned Map View projected coordinate reference system if the data lies within the projected CRS bounds.