The graticule described is for a polar aspect.
Meridians: Equally spaced straight lines intersecting at the central pole. The angles displayed are the true angles between meridians.
Parallels: Unequally spaced circles centered on the central pole. Spacing increases gradually away from this pole.
Pole: The central pole is a point; the other pole is not shown.
Symmetry: About any meridian.
This is a perspective projection on a plane tangent at the center point from the point antipodal to the center point. The center point is a pole in the common polar aspect, but can be any point. This projection has two significant properties. It is conformal, being free from angular distortion. Additionally, all great and small circles are either straight lines or circular arcs on this projection. Scale is true only at the center point and is constant along any circle having the center point as its center. This projection is not equal-area.
There are no standard parallels for azimuthal projections.
The polar aspect of this projection appears to have been developed by the Egyptians and Greeks by the second century B.C.
Data greater than 90º distant from the center point is trimmed.
landareas = shaperead('landareas.shp','UseGeoCoords',true); axesm ('stereo', 'Frame', 'on', 'Grid', 'on'); geoshow(landareas,'FaceColor',[1 1 .5],'EdgeColor',[.6 .6 .6]); tissot;