Complex sentence: A town plan may be constructed as an exact scale drawing but for larger areas a map projection is necessary and "no" projection can represent the Earth's surface at a uniform scale: in general the scale of a projection depends on position and direction.
Split into simpler sentences: A town plan may be constructed as an exact scale drawing, but for larger areas a map projection is necessary and no projection can represent the Earth's surface at a uniform scale. In general the scale of a projection depends on position and direction.