"This website provides an introduction to digital collections designed for education. They are mainly aimed at university students, researchers and librarians but many of the online archives are open to anyone. The collections cover areas such as history, social sciences, or science and engineering and include, for example, journals, newspapers and images."
Population density
Population density is the number of people in a given area (usually given as persons per sq. km.). To find this figure the total population is divided by the area.
Density can be shown on a choropleth map which shows the average density across regions. This is easy to read but disguises major population concentrations.
Check you know the main principles by reviewing the list of different topic areas, either click on the topic heading to quick learn the whole topic or pick individual principles to brush up.
Clear, but just text - could be used as a reference for some independent learning (homework) - does include an 'Action' and has some side links for further study.