Boundaries

Rhumb line and Great-circle_distance

Great-circle_distance

Rhumb_line

Straight and curved in the city

The urban plan view showing the intersection of several straight and curved roads

Straight and curved rivers

Leopold and Wolman (1957) have classified different river styles. This classification is essentially based on the shape of the river channel, as it appears on aerial photographs.

Straight rivers have a low sinuosity index. Meandering rivers have instead a channel characterized by sinuous curves.

 Take from: http://www.geo.uu.nl/fg/palaeogeography/results/fluvialstyle