Right Angle Draw Mode and Ortho Draw Mode may be selected to specify draw modes in Global Mapper.
When drawing a line or area feature, after the first two vertices are defined, the third vertex must be 0, 90, 180 or 270 degrees from the initial line segment. This will result in an area or line that is composed of right angles.
When drawing a line or area feature the first vertex can be placed anywhere and from there the next vertex must be at an angle of 0, 90, 180 or 270 degrees from the initial vertex. All subsequent vertices also follow this rule. This will result in an area or line that is composed of right angles with respect to North, i.e. orthogonal to the projection.