What is a Predominance map?

An election map is an example of a predominance map. An election map simply tells you which of two or more candidates has the highest total vote count.

For example, this map shows the predominant count of votes for President in North Dakota voting precincts from the 2008 election. Darker colors indicate a higher predominant vote for that party. Lighter colors indicate that party barely won the precinct. White represents an exact tie.

Republican votes are in red

Democrat votes are in blue

A campaign manager can instantly see in this map which precincts have a strong base for each party, and which precincts were more contested.

Smart mapping in ArcGIS lets anyone quickly discover patterns in data and make meaningful maps from them. You can now use smart mapping to analyze multiple columns of related data, in order to determine which has the highest, or predominant, value for each feature. Try a predominance map any time you see multiple columns of data that share a common subject and unit of measurement.

To create this map, simply choose two or more numeric attributes to compare. The Predominant Category map style determines which attribute has the largest value for each record, and shades the map symbols based on that predominance.

An Election Map

Not all precincts are equal, however, in terms of population or voter turnout. This map helps address that reality, by using symbols based on the size of the total vote in each precinct. It still shows the predominant vote for President in North Dakota from the 2008 election, but a campaign manager now sees the precincts with the largest total votes, which party is predominant, and by how much.

Republican votes are in red

Democrat votes are in blue

Click the map to see vote details.

To create this map, simply choose two or more numeric attributes to compare. The Predominant Category & Size map style determines which attribute has the largest value for each record, and shades the map symbols based on that predominance.

Predominant Education Level

It is true that nearly every county has people of every education level present, but some have more of one level than others. This map shows the predominant education levels in U.S. counties. The map's colors are based on the most popular educational attainment level among each county's adult population (age 25 and older). The map reveals interesting rural, suburban and urban patterns across the nation.

Graduate Degree

Bachelor's Degree

Some College

High School Grad

Certain counties stand out because the count of people within the predominant education level is much larger than other levels of education.

Understanding the strength of a predominant attribute is useful. The Predominance map style uses transparency to help communicate how predominant one attribute is relative to the others. A strong green color indicates a very predominant situation, where one attribute is significantly higher than all others considered. A weak, mostly transparent color indicates that the predominant value has a slim margin over the next highest value.

Similarly, check out another education level predominance map in Los Angeles using Census Tract centroid points instead of county polygons.

Map Each Sale's Revenue vs. Cost

Predominance maps can also use size to show the magnitude of what's being mapped.

This map shows individual sales of furniture delivered to homes in the Los Angeles area. A sales manager can look at this map to immediately spot which is higher for each sale: the cost, or the revenue. The size of the symbol reflects the relative magnitude of each sale, so we can easily spot some concerning sales near Westwood worth investigating.

In this example, the size of the map symbols represent the sum of costs and revenues.

Make Comparisons Over Time

Are things better now than before? Predominance can be used to show growth and decline over time by comparing the same variable from two different years.

This map compares traffic counts in 2006 and 2011. Some roads had more annual daily traffic in 2006, while others had more in 2011.

The size of the roads showcases the overall traffic between the two years. Larger segments have more everyday traffic than segments that are smaller.

To make this map, select the Predominant Category & Size map style in ArcGIS Online, choose the attributes to compare, and adjust the size of the lines as desired.

Young Money in Manhattan

Most people experience their "prime income-earning years" in their 40s, 50s or 60s. This map shows that, for some areas in New York, the highest income category the U.S. Census reports is experiencing a youth movement.

Householder Age 25-34 w/ Income $200,000+

Householder Age 35-44 w/ Income $200,000+

Householder Age 45-54 w/ Income $200,000+

Householder Age 55-64 w/ Income $200,000+

In this map, color indicates the predominant age group for those households that earn $200,000 or more per year in income. It checks four columns of data in this Census tract layer, then sets the color based on the predominant householder age range, for households making $200,000+ annually. The transparency showcases the strength of the predominance. Predominant values with a significant count of population within the largest category are shown with less transparency.

Get Started

To start making predominance maps, add a layer to your map that has two or more attributes that are related, and have the same unit of measure. For example, an election map containing total votes for two or more parties is perfect. Choose the attributes you want to compare, and the Predominance map style analyzes your columns of data to produce an initial map showing the predominant value found in each feature. Then tune the map to suit your desired colors, sizes, and transparency settings.

Visit our help pages to get started and learn these new techniques today.