Geostrophic winds exist in locations
where there are no frictional forces and the isobars are
striaght. However, such locations are quite rare.
Isobars are almost always curved and are
very rarely evenly spaced. This changes the geostrophic winds
so that they are no longer geostrophic but are instead in
gradient wind balance. They still blow parallel
to the isobars, but are no longer balanced by only the pressure gradient
and Coriolis forces, and do not have the same velocity as geostrophic winds.