Reading maps as evidence

Overview

What to check on a supplied map before drawing anything from it, using the scale to produce evidence rather than an impression, and where a choropleth misleads.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What can a map in a resource booklet tell you that no other resource can?

   Model answer

   Spatial relationships. A map shows where things are in relation to each other - how close housing is to a proposed site, which settlements lie downstream, how the land use pattern is arranged, where relief rises and falls, what roads and railways connect the site to. Those relationships are usually what determine who is affected and how feasible an option is, and they cannot be recovered from a table of figures.

2. 2

   What should you check on any supplied map before you start drawing conclusions from it?

   Model answer

   The title, the key, the scale, the north arrow, the date and the extent. The key tells you what the shading or symbols mean; the scale converts map distance into ground distance; the date tells you whether the land use shown still exists; and the extent tells you what has been cropped out, which may include the very communities that would be affected.

3. 3

   How do you use a map's scale to produce evidence rather than an impression?

   Model answer

   Measure and convert. Instead of writing that the site is close to housing, use the scale bar to state that the nearest housing is roughly 400 m from the boundary, or that the diversion adds about 3 km to journeys. A distance in metres or kilometres can be weighed against noise, access or cost; a word such as near cannot, and different readers would picture different things.

4. 4

   What are you looking for in the contour pattern on a map of a proposed flood or development scheme?

   Model answer

   Height and steepness. Closely spaced contours mean steep ground, which raises construction cost, increases runoff and speeds water to the channel; widely spaced contours on a valley floor mark the floodplain, where inundation is likely and where new building is most exposed. Contours also show which settlements sit above the risk and which do not, which often decides who benefits from a defence and who is left out.

5. 5

   Why can a choropleth map in a resource booklet mislead you about the pattern it appears to show?

   Model answer

   Because it averages the value across each whole unit, so internal variation disappears - a district shaded as prosperous can contain severe deprivation. Large units draw the eye more than small ones regardless of the population involved, and the pattern shifts if the class boundaries are drawn differently. Use it for the broad geography and look for a data table to support any specific claim.

6. 6

   What are the general blind spots of maps as evidence?

   Model answer

   A map is a snapshot at one date and a selection made by whoever drew it: features are generalised, some are omitted, and the boundary of the sheet cuts off whatever lies beyond. It shows where things are, not how intense, how busy, how valued or how contested they are. It cannot tell you what residents think, how a place feels, or whether a land use shown is still active.

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