Which direction should I run my vineyard rows?

Grape rows are ideally oriented in a north-south direction for maximum sunlight interception. However, slope may dictate a different row orientation to avoid operating equipment across slope or in cases where rows running down slope would lead to severe soil erosion. Likewise, land dimensions may make it more efficient to run rows in a direction other than north-south. For instance, if a rectangular piece of property lays east-west, a north-south row orientation would lead to a large number of short rows each with added expense for end-post assemblies, and a higher percentage of the land dedicated to headlands.