Most lessons will include a Concept Gallery section that is based on content that you must know before completing the various projects and assignments. View this lesson's concepts via the links below or via the lesson navigation on the side.
Briefly review the section on Surfaces in the Lesson Four Concept Gallery. Looking at Figure 4.cg.1, remind yourself of the differences between discrete and continuous phenomena. Also recall how phenomena can change from abrupt to smooth in terms of their spatial dependence. In Lesson Four we discussed the choropleth map representation, which is useful to represent continuous phenomena (i.e. it exists throughout the space mapped) that changes abruptly at observation boundaries. In this lesson we are going to review additional map representations, two of which (graduated/proportional symbol maps and dot maps) are best used to represent discrete observations, e.g. point data. The observations can be based on actual point data (e.g. locations of weather stations) or conceptual point data, where observations over an area are aggregated (e.g. counts of people in enumeration units).