To understand the purpose of precis sketches and use the skill in context
Vertical, Oblique, Ground level,
Precis = The word precis means a simplification or a summary of something. Therefore a precis map is a summary map.
Sketches in Geography can be drawn at different angles. The most common one we know is Vertical (otherwise known as "birds-eye view"). This is how we view most maps. We are also familiar with Ground Level as that is how we see the world! Oblique Angle is viewed not from over top of but on an angle looking down.
Below are examples of these different views and what they are used for. Note the buildings are a little out of date!
Vertical Angle
This is used for maps, photographs and precis sketches
Oblique Angle
This is used for photographs and precis sketches
Ground Level
This is used for photographs and field sketches