GEOGRAPHIC SKILLS: DOT MAPS

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. SKILLS DOT MAPS 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).

5. 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 .

6. 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.

7. 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.

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

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

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

11. STEPS TO CONSTRUCT A DOT MAP Obtain a base map of the area or administrative regions you wish to show. Study the data to be mapped and decide on a dot value (should be a rounded number). Determine the number of dots required for each administrative region. 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. Place the correct number of dots within each administrative boundary as determined in Step 2.

12. TASK