Meridians: Equally spaced straight parallel lines.
Parallels: Unequally spaced straight parallel lines, perpendicular to the meridians. Spacing increases toward the poles.
Poles: Straight lines equal in length to the Equator.
Symmetry: About any meridian or the Equator.
This is a perspective projection from a point on the Equator opposite a given meridian onto a cylinder secant at the 30º parallels. It is not equal-area, equidistant, or conformal. Scale is true along the standard parallels and constant between two parallels equidistant from the Equator. There is no distortion along the standard parallels, but it increases moderately away from these parallels, becoming severe at the poles.
For cylindrical projections, only one standard parallel is specified. The other standard parallel is the same latitude with the opposite sign. For this projection, the standard parallel is by definition fixed at 30º.
This projection was first described in 1937, when it was used for maps in the Bolshoi Sovietskii Atlas Mira (Great Soviet World Atlas). It is commonly abbreviated as the BSAM projection. It is a special form of the Braun Perspective Cylindrical projection secant at 30ºN and S.
This projection is available only on the sphere.
landareas = shaperead('landareas.shp','UseGeoCoords',true); axesm ('bsam', 'Frame', 'on', 'Grid', 'on'); geoshow(landareas,'FaceColor',[1 1 .5],'EdgeColor',[.6 .6 .6]); tissot;