Maps and graphs Maps
Well-drawn maps of a suitable scale and type will significantly improve the overall quality of a report. Always remember to include a title, key, north arrow and scale. It is fine to use computer-generated maps, but you should also include some hand-drawn versions to show originality and your cartographic skills.
Isoline maps
Isolines are lines that join points of equal value (see Figure 1). The best example is contours, usually used to join points of equal height on maps. You may also have seen them used to represent temperature or air pressure. Decide on suitable intervals for the isolines by looking at the range of values. Usually a fixed interval is chosen. Constructing the lines is the hardest part of the exercise and should be done by ‘interpolation’.
Fig. 1. Isoline map (interpolated) showing pedestrian values for a town centre. The dots indicate count points.
Choropleth
Shaded or choropleth1 maps show differences in data area by area, they are good for making comparisons between places (see Figure 2). An example might be county maps showing levels of unemployment or areas of high ground.
T
o
make your own choropleth map, you will first have to divide your data
into equal categories (up to a maximum of about five intervals). Then
make a key on your base map and decide on your shading colour. It is
important to use just one colour in shades from light to dark. Use
the darkest shade of colour to indicate the highest numbers and vice
versa.
Topological maps
A topological map2 is one where distances between places have been altered and routes simplified, but the position of one place relative to another is still recognisable (see Figure 3). The London Underground map is a good example. Topological maps can also represent travel time (actual or perceived) rather than distances. They are useful when considering the accessibility of certain places or areas.
Fig. 3. Topological map showing access time to five destinations. This can he based on actual or perceived travel time.
Proportional flow maps
On proportional flow maps3, the width of lines is proportional to the volume or size of movement between places (see Figure 4). They are particularly useful for displaying the results of traffic flows, but can be used to indicate any movement across a space.
Fig. 4. Proportional flow map for traffic volumes in a town center
Dot maps
Dot maps4 show the distribution of items such as people, houses or plants (see Figure 5). The pattern of dots may also be analysed statistically, e.g. by nearest neighbour analysis. When constructing dot maps consider the dot size – this can be used to generate a hierarchy based on the relative sizes of populations.
Fig. 5. Dot distribution map (including isolines). This example shows the sphere of influence of visitors to a honeypot site, based on questionnaire data.
Graphs
Unlike most maps, graphs can be produced using computer software such as Excel or Lotus. Using graphs can also demonstrate your skills. You need to be very careful in selecting the most appropriate type of graph from the computer menu, not always the first one that appears on the drop-down list. Avoid some of the more showy three-dimensional graph types which can be complex for the reader to interpret.