On a planimetric map, the is used to determine the actual distance between two points.

The answer in this question is scale. The scale is used to determine the actual distance between two points in a planimetric map. This map only represents the horizontal position of features. This is also called by others as the line map.  This is usually consisted of man-made and natural features. These are from aerial shots by the use of modern technology. This map’s common features are street and water centerlines, sidewalks, culverts, utility lines, building footprints and vegetation. Sometimes, there are also other useful data attached in this map like titles of the properties, owner, assessed value, etc. It is because of these, this map becomes a storage of valuable data which can be easily and quickly accessed. 

i wanna say it’s between b and d, leaning more towards b.

measure their densities same density, same sub