How Do You Draw a Choropleth Map?

Chloropleth maps present the variation of a certain measurement over physical space. Each unit of space represents a single point of normalized data. These maps allow for easy visual comparison of a certain factor, like per capita income or fertility rate. Make a chloropleth map by dividing a standard map into equal units that correspond to gathered data, converting all data points to the same unit of measurement, and assigning a level of scaled physical representation for the data tied to each unit.

1. Divide a map

Get a map that contains the physical space to which your data corresponds. Divide the map by areas for which the data was collected. For example, divide a state by counties, or a city by neighborhoods, depending on the comparison you want to make.

2. Normalize the data points

Convert all points of data to the same units of measurement. If you have measurements of income for each family in a city, convert the measurements to the same currency and time frame, such as annual income in USD.

3. Assign a level of representation for each unit

Make a scale to physically represent each data point. Use color progression from light to dark to represent magnitude, with light representing least and dark representing greatest. Each unit of space on the map is assigned a single, uniform color gradient based on its corresponding data point.

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