A bivariate map portrays two variables, which represent two different phenomena simultaneously on a map. Bivariate maps enable users to visualize the spatial relationship between two variables, such as the relationship between population density and crime density, or between rainfall volume and forest density.
The following workflows describe how to create a quantitative bivariate map in ArcMap. Depending on the suitability, select one of the options below:Option A - Categories: Unique values, many fields
This option creates a layer category by combining up to three fields. The combination of these fields is symbolized by the color ramp to represent each unique combination.
Note: For a large set of data consisting of many combinations, this method is not intuitive in portraying the relationship between different variables. There are a few alternatives to make the pattern more apparent. This includes, adding labels on the map to define the data, combining similar categories into one to produce a lesser number of combinations, or proceeding with another method that is more intuitive and representative of each variable.
The image below shows a quantitative bivariate map using the Categories: Unique values, many fields option. Each unique color represents a different combination between two variables: the house theft and vehicle theft occurrences.
Dot density represents data as point data on a map. Each dot represents a certain value or a certain size, as specified by users. The placement of these dots is random and is not representative of the feature locations. The occurrence density is represented by the proximity of these dots.
Note: In differentiating between two or more variables, it is best to keep the colors in high contrast between one another.
Note: Optional fields include changing the Background color, clicking the Properties button to select Dots placement and Masking option, and maintaining the appearance of dot densities.
Note: To maintain the density of the data, check the Maintain Density By check box and specify either to maintain by Dot Value (when zoom in, number of dots increase) or Dot Size (when zoom in, size of dots increase).
The image below shows a quantitative bivariate map using the Quantities: Dot Density option. Each dot represents 50 theft occurrences. The green dots represent the vehicle theft occurrences while the blue dots represent the house theft occurrences.
The usage of charts in ArcMap symbology is to portray quantitative representations of multiple variables on the same map.
Note: To present a variable as part of a whole, use either the Pie or Stacked chart (check Fixed Length) option. To present relative amount between variables, use either the Bar/Column or Stacked chart (uncheck Fixed Length) option.
Note: Optional fields include changing the Background color, defining the Normalization field (for Bar/Column or Stacked charts), specifying the chart Properties, and determining the chart Size.
The image below shows a quantitative bivariate map using the Charts: Pie option. The green color portion represents the vehicle theft occurrences while the blue portion represents the house theft occurrences.
This method allows users to represent specified categories by using combination of color ramp (first variable and/or second variable) and symbol markers (second variable) to portray two different variables.
The image below shows a quantitative bivariate map using the Multiple Attributes: Quantity by Category option. Different hues of blue color represent the number of house theft occurrences (darker color represents higher number of occurrences), while different size of green dots represent the number of vehicle theft occurrences (larger dot represents higher number of occurrences).