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Altitude that is at least 500 feet above any obstacle or terrain
In aviation (particularly in air navigation), lowest safe altitude (LSALT) is an altitude that is at least 500 feet above any obstacle or terrain within a defined safety buffer region around a particular route that a pilot might fly. The safety buffer allows for errors in the air by including an additional area that a pilot might stray into by flying off track. By flying at or above this altitude a pilot complies with terrain clearance requirements on that particular flight leg.

On Canadian IFR High and Low Level charts, area minimum altitudes (AMA) are published for quadrangle areas, which provide a buffer beyond the VFR maximum elevation figure. The AMA is the lowest off airway altitude to be used under instrument meteorological conditions (IMC) that will provide a minimum vertical clearance of 1,000 feet (AGL), or in designated mountainous terrain 2,000 feet above all obstacles located in the area specified, rounded up to the nearest 100 foot increment.

Since VFR flights are not necessarily conducted on straight lines between ground based radio navigation transmitters, the altitude restrictions for IFR flights are not applicable. Instead, a VFR flight can be conducted using pilotage, watching landmarks to determine position and desired direction. In this situation, the minimum reception altitude becomes moot, and the over riding concern is for obstacle clearance. Pilotage in the United States is usually accomplished with the use of sectional charts, which show the ground with considerable accuracy, both for terrain levels and for man made objects. The charts are marked with World Geographic Reference System or GEOREF grids, and at the center of each grid square a number shows the elevation (MSL) of the highest obstacle within that grid (the maximum elevation figure or MEF). Thus a pilot is alerted of how high he must fly while traversing that grid to assure clearance of all possible obstacles. Then it is up to the pilot to select a cruising altitude which will provide the required clearance above those obstacles. On sectional charts, man made obstacles less than 200 feet in height may not be shown.