# Choropleth mapping

Choropleth Mapping uses a thematic map displaying a quantitative attribute using ordinal classes which are assigned a symbolize feature and is applied over an area.They are based on the same data and spatial units but can represent different patterns due to the choice of class interval. They usually present population data at a large or small scale for example sex ratio in a province would be classified as small while population of school children in census tracts would be large.Choropleth mapping can be abused, by using different techniques to create a map and can be easily misrepresented. User must be aware and observe critically before concluding to a decision. There are unfortunately three common problems with choropleth mapping:
Choice of shading pattern, Choice of classification system, and Choice of spatial unit.

Use the universal code of 'darker is greater' when specifying shading patterns, and with colors bright colors represent higher values.

Classification System:
Must specify number of classes and class intervals in the map.
-The greater the number of classes used, makes the map more confusing to intrepid.
-Max of 5 classes is sufficient to display data.
-There are four common ways to specify class intervals: equal interval, percentile, and natural breaks.
-Equal Interval: Splits data into user-specified number of classes of equal width.
-Percentile: Data divided so that equal number of observations fall into each class.
-Natural Breaks: Splits data into classes based on natural breaks using a commonsense method when interpreting data.
-Manual: Gives the user freedom to set classes and number of breaks within the data.
Choice of Spatial Unit:
Usually out of users control. Extremely hard to go beyond minimum resolution or translate data in other non matching units.
Choice does exist with change of data into larger spatial units. census tracts --> census districts.
Amalgamation of data can lose information bu masking internal pattern and variation that could be potentially important to the user.
Part of the Spatial Unit is MAUP (Modifiable areal unit problem) where boundaries of spatial units act to hide underlying patterns in data.
Ecological fallacy problem associates with MAUP. And occurs when it is inferred that a data for study area applies to indv. within an area.

For a Choropleth map a user needs a legend to make sure correct interpretation is seen. It tells the user what shading patterns, colors, lines, and point symbols mean. As well it gives information about the class interval system used. Also annotation should be used to bring the map to life by giving information by textual or graphical techniques that labels the map and features within it. Annotation consists of a map title, legend, North arrow, and other specific labels such as names to points on a map. Choropleth mapping is representing science as art. Using technical decisions about scale, generalization, and reference systems by representing them by Artistic decisions to make the map appear appeasing. Using this user friendly method helps communicating spatial information to others such as for government policy making, or business management.

In relation to the case study you could use it for showing population density's of grizzly bears kills in different regions of BC by representing them in color. Using Natural breaks to represent the population in intervals.