Surface weather analysis isotherms (lines of equal temperature), and isotachs (lines of equal wind speed) are drawn. The abstract weather symbols were devised to take up the least room possible on weather maps. A synoptic scale feature is one whose dimensions are large in scale, more than several hundred kilometers in length. Migratory pressure systems and frontal zones exist on this scale. Centers of surface high- and low-pressure areas that are found within closed isobars on a surface weather analysis are the absolute maxima and minima in the pressure field, and can tell a user in a glance what the general weather is
Lambert azimuthal equal-area projection intersects the unit sphere in exactly two points, one of which is on the lower hemisphere "z" ≤ 0. (Horizontal lines intersect the equator "z" = 0 in two antipodal points. It is understood that antipodal points on the equator represent a single line. See quotient topology.) Hence the directions in three-dimensional space correspond (almost perfectly) to points on the lower hemisphere. The hemisphere can then be plotted as a disk of radius using the Lambert azimuthal projection. Thus the Lambert azimuthal projection lets us plot directions as points in a disk. Due to the equal-area property of the projection,