Data
In our maps, you draw your own districts and communities from a given set of units or building blocks. Common building blocks that you'll see in our modules are precincts, block groups, or blocks. Precincts are the smallest unit at which vote counts are reported. (Usually these correspond one-to-one with polling places, where you actually go to cast a vote.) Therefore, precincts are the smallest unit to use when you care about accurate election results. In a map built from precincts, you can explore recent election results and visualize the partisan lean in your state. Precinct level data can be notoriously difficult to collect! In Districtr v2, we use Census VTDs, which are approximations of precinct boundaries collected by the Census and adjusted to be constructed out of blocks.Blocks and block groups are units created by the United States Census Bureau with input from individual states. Blocks are the smallest geographic unit published by the Census Bureau, and attempt to fit neatly into the geographic features of their surroundings (e.g. interstate highways, rivers, city blocks etc.) while block groups are formed by grouping blocks together such that no two block groups share a block. The Census Bureau publishes geographic products, including revised block and block group geographies at least every decennial census, in accordance with Public Law 94-171.The Decennial Census is the nationwide tallying of every person living in the United States, and has been conducted every ten years since 1790. The final Census product is an extremely large dataset, with more than 18,000 tabulated variables, and is published at the block level. The American Community Survey (ACS) is another large dataset produced by the United States Census Bureau. To collect data, the Census Bureau surveys approximately 3.5 million households across the United States each year, and produces two data products from households across the United States each year, and produces two data products from this survey: 1-year estimates and 5-year estimates. 1-year estimates are estimated population statistics published for Census-designated areas with 65,000 people or more, and so is unsuitable for redistricting. The 5-year estimates are estimated population statistics, including income and some demographic data, and are published at the block group level regardless of population.To compute the demographic categories like "Black" and "Asian" in Districtr v2, we use collections of columns from the Decennial Census. You can read more about exactly which columns we use here. On the backend, all of our data comes from the Data and Democracy Lab Redistricting Lab's gerrydb database, which stores all sorts of geospatial data.
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