The kinds of information collected for a contextual analysis involve an inventory of existing and projected site conditions.
Keep in mind at all times that this is not a design response but rather finding out all that can be done about the site and how we represent the facts. We must be sure to make reference drawings as simple as possible, data to be recorded over must be graphically bolder and more important than the referent information. For that matter, it is useful to diagram the site information as we collect it. Whether we refine the diagram later for presentation.
The following quick thumbnails should help to kickstart the development of your own vocabulary of diagrammatic forms so that they can be used as an effective graphic shorthand for documenting site conditions. Take them as a first template.