Grids

"Grids," that is to say patterns of squares, are super-imposed on some maps to enable a point to be quickly defined by co-ordinates.

Several sorts: large non-rotating ribbon arch kite (windbow), rotating ribbon kite, and kite with main sails made up of grids and meshes of ribbons (latticework kites).

Minimum En route Altitude (MEA) is arc around navaid.
Emergency Safe Altitude (ESA) is used by military.
Minimum Off-Route Altitude (MORA) by Jeppesen grids.
Off-Route Obstacle Clearance Altitude (OROCA) Government charts.

See also: Aircraft, Speed, Section, Wind, Direct