Value-by-alpha is achieved by using two layers in your table of contents in ArcGIS Pro. It can also be made directly inside ArcGIS Online map viewer.
Sometimes election maps hide important factors, most crucially, population. We love how this map uses a technique called “value-by-alpha” to overlay a second layer that varies transparency by population density. It gives a better idea of the popular vote for the 2012 US presidential election. Areas with more voters pop with bright colors while areas with relatively low populations recede into muted tones.
Without the value-by-alpha layer this map would be a straight red/blue map showing counties that voted Democratic and those that voted Republican. It wouldn’t tell us much about the real voting patterns. In fact, it would suggest a Republican landslide. The value-by-alpha layer gives nuance to the map, immediately bringing highly populated counties into focus and diminishing the counties with fewer voters.
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If you liked this map, check out these other Maps We Love that explore similar topics.