One feature which is different on upper level maps is that meteorologists are no longer looking at the surface where the pressure varies. In this case, instead of pressure given on a station model, height above the surface is given, in the same location on the model where the pressure was. For both these, the first digit is a 1 or 0, whichever brings you closer to 10,000. This height is also sometimes referred to as the geopotential height. Since typically lower heights represent lower pressure, and higher heights represent higher pressure, contouring heights can help us see the flow, like isobars do at the surface.
Contours are now no longer of constant pressure, but of constant height .
While the flow behaves similarly in the upper levels, there are some differences in how the wind flows at the upper levels as compared to the surface. Winds behave the way they do due to forces that act on them. If you had a baseball, it s not going to move itself, you must exert a force on it to get it to move. The air in the atmosphere acts the same way. Different forces are useful in determining the winds at different levels, so we will start with what we know, the surface winds.