A(n) shows areas of high or low height, and a(n) shows areas of high or low pressure.

a isobaric chart; surface map
b surface map; isobaric chart

B surface map; isobaric chart

Explanation:

A surface map is a map used in weather analysis to view the geographical areas from the weather perspectives through the use of ground-based stations. This map shows all the surface phenomena like the winds, rainfall and cloud cover, etc. The isobars show the variation in atmospheric pressure over the high and lower pressure areas when the air pressure is lower the bars are spaced and when the pressure is higher the bar is closely spaced. Thus the isobaric charts show us the areas that are well defined in terms of equal areas of atmospheric circulation of the map. Displacement of warm and cold air also tells us the type of formations of pressure formations

Europeans are more concentrated in urban areas.