Oblique aerial photographs are split into two types, low oblique and high oblique:

Low Oblique: The photographs is taken with the camera inclined about 30° from the vertical . It is often used by the military to study an area before an attack or as a substitute or supplement for a map. A low oblique has the following characteristics:

1. It covers a relatively small area 2. The ground area covered is a trapezoid, although the photo is square or rectangular 3. The objects have a more familiar view, comparable to viewing from the top of a high hill or tall building 4. No scale is applicable to the entire photograph, and distance cannot be measured. Parallel lines on the ground are not parallel on this photograph; therefore, direction (azimuth) cannot be measured 5. Relief is discernible but distorted 6. It does not show the horizon

Relationship of low oblique photograph to the ground (www.map-reading.com)

High Oblique: Here the photograph is taken with the camera inclined about 60° from the vertical and it is often used in the making of aeronautical charts. A high oblique has the following characteristics:

1. It covers a very large area (not all usable) 2. The ground area covered is a trapezoid, but the photograph is square or rectangular 3. The view varies from the very familiar to unfamiliar, depending on the height at which the photograph is taken 4. Distances and directions are not measured on this photograph for the same reasons that they are not measured on the low oblique 5. Relief may be quite discernible but distorted as in any oblique view. The relief is not apparent in a high altitude, high oblique 6. The horizon is always visible.

Relationship of high oblique photograph to the ground (www.map-reading.com)