GEOGRAPHIC SKILLS: DOT MAPS. A dot distribution map, or dot density map, is a map type that uses a dot symbol to show the presence of a feature or a phenomenon. Dot maps rely on a visual scatter to show spatial pattern.

1. THEMATIC MAPPING TECHNIQUES

2. WHAT IS A DOT MAP?
• A dot distribution map, or dot density map, is a map
type that uses a dot symbol to show the presence of a
feature or a phenomenon.
• Dot maps rely on a visual scatter to show spatial
pattern.

3. Acres of Harvested Wheat in Illinois in 2012

4. DOT (DISTRIBUTION)
• A dot map uses dots to show the distribution (relative
density) of geographic phenomena between different
regions on a map.
• Each dot on a dot map represents a single feature or a
quantity (number value).

6. OVERALL DISTRIBUTION
• When viewed as a whole, a dot map will give its
reader an impression of the overall distribution
(spread) of geographic phenomena throughout the
mapped area.

7. MEDICAL GEOGRAPHY
• Display of discrete data in the form of points in a map
can provide convincing evidence related to medical
geography.
• During the mid-1850s, cholera was a major concern.
• When a large outbreak occurred in London in 1854, Dr.
John Snow created a dot distribution map that settled a
debate between two schools of thought that cholera is
transmitted not through the inhalation of infected air,
but through the ingestion of contaminated water or
food.

8. Original map by John
Snow showing the
clusters of cholera
cases in the London
epidemic of 1854. The
pump is located at the
intersection of Broad
Street and Little
Windmill Street.

9. COMMON USE
• Dot maps are most commonly used to compare
population densities across a region.

10. HOW TO DO IT
1. Identify the geographic feature or phenomena being
mapped.
2. Verify the dot value. This can be done by reading the map’s
legend.
3. Identify the scale of the administrative regions shows on
the map (neighbourhoods, census areas, states or
countries).
4. Calculate the total value of features in each area of the
map.
5. Describe the distribution of the feature both within and
between different areas.

11. COMMON PATTERNS FOUND ON A MAP
1. CLUSTER – A group of people or features positioned or
occurring close together.
2. SCATTERED OR DISPERSED – Occurring or distributed over
widely spaced and irregular intervals.
3. GRID – A network of regularly spaced lines that cross one
another at right angles.
4. LINEAR – Arranged in or extending along a straight or
nearly straight line (river or coastline).
5. CONCENTRIC – Circles that share the same centre, the
larger surrounding the smaller.
6. RADIAL – Lines running directly from a centre point.

13. STEPS TO CONSTRUCT A DOT MAP
1. Obtain a base map of the area or administrative regions
you wish to show.
2. Study the data to be mapped and decide on a dot value
(should be a rounded number).
3. Determine the number of dots required for each
administrative region.
4. Decide on an appropriate dot shape and size. As a general
guide, dots that are too small produce an overly sparse dot
pattern which is not very precise.
5. Place the correct number of dots within each
administrative boundary as determined in Step 2.

14. TASK