Drawing 2020 Maps
This note describes our plan for enabling you to start drawing maps for the upcoming redistricting cycle even though the 2020 census counts are delayed until September.
In a nutshell, we’ll let you draw maps using 2020 shapes, and then we’ll add the 2020 census data later. There’s also one major feature that is only available for 2020 maps 🤓.
The following sections describe the major elements of our plan:
- 2020 vs. 2010 maps
- Creating new maps using 2020 shapes
- Converting existing maps to use 2020 shapes
- Importing maps
- Official 2020 maps
- Operational contiguity, and
- What happens when 2020 data becomes available
This will be a big transition, and we want to help you get started on it as soon as possible.
2020 vs. 2010 Maps
Until now, all maps in DRA 2020 used 2010 census shapes, thus no other options were surfaced. Now that 2020 shapes are available, you can draw maps either with the old 2010 shapes or the new 2020 shapes. The latter is now the default, since new districts must be defined in terms of 2020 as opposed to 2010 census blocks.
When comparing maps yourself — or when we do it for the Notable Maps on state pages, for example — the critical thing to understand is that maps drawn with 2020 shapes and the maps drawn with 2010 shapes are disjoint sets even if you drew a map using 2010 shapes with an eye toward the 2020 redistricting cycle. In other words, you can’t compare maps drawn with the two different kinds of shapes. So, if you want a map that you’ve drawn with 2010 shapes to be considered in & compared to the pool of 2020 maps, you have to convert it to use the 2020 shapes. (See “Converting Existing Maps” below.)
Creating New Maps
When you click on New Map, the dialog will look a little different:
- Shapes — You will now have a choice of shapes: 2020 Precincts (default) or 2010 Precincts
- Plan Type —You will also have a choice of types of maps: Congress, State Senate, State House, or Other. The last lets you experiment, e.g., with local redistricting.
- District Count — As before, a field will specify the number of districts. However, this will now be keyed off of the type of plan you’ve chosen, and it will use our best guess estimates of the new congressional apportionments. As before, you can change the number of districts, if you want.
The other big change here involves the data. Beyond the shapes, there are three datasets associated with each map:
- Census — The total population counts to use.
- Voting Age — The voting age population counts to use.
- Election — The election data to use.
These are shown in the Data Selector.
Since the 2020 census data isn’t available yet, we are using the latest estimates — the 2014–2018 ACS 5-year Estimates (what we refer to as “2018 ACS 5-year” or simply “2018 ACS”) — for both the Census and Voting Age datasets. When the 2020 census data is released, these choices will them up.
We have migrated most election data from the 2010 shapes so it is also available when using 2020 shapes. The default Election dataset will continue to be our election composite. Note: We’ll incorporate 2020 election data into it as we get it, but that’s a separate issue.
Converting Existing Maps
When you open a 2010 map, you’ll see a yellow “Convert to 2020” button in the upper right corner of the map.
When you hover over the button, the tooltip says “Open dialog to convert 2010 Shapes to 2020 Shapes.” You don’t have to convert your existing maps to use 2020 shapes — in fact, you should probably only convert the ones that you want to be considered in the 2020 mix, as opposed to all your explorations using 2010 shapes! — but when you click on the button, you’ll get this dialog
Converting a map makes a copy of that map — your original map is not changed. That’s why you need to name the converted map.
As with creating new maps using 2020 shapes, your converted map will use the 2018 ACS estimates for the Census and Voting Age datasets Election dataset that your original map does.
Note: The mapping between 2010 shapes and 2020 shapes is not always exact, and new 2020 maps don’t have any split precincts, so the converted map may approximate how the precincts were assigned to districts in your 2010 map.
Importing Maps
You can also import block-assignment files that define maps in terms of 2020 blocks.
Official 2020 Maps
We imported the latest congressional & state legislative maps into the Official Maps collection.
To see them, click on “My Maps” on the left side of in the list of maps and then choose “Official Maps.” The latest official maps are named like this, using Maryland as an example:
- MD 2020 Congressional
- MD 2020 State Senate, and
- MD 2020 State House
The previous maps instead have 116th or 2018 in their names for the congressional and state legislative maps, respectively.
Operational Contiguity
The shapefiles for states can sometimes make districts look not contiguous (“discontiguous”) when they are considered connected in real life. This happens principally with water, islands in particular.
We when released 2020 shapes, we hadn’t yet addressed these issues for the 2020 shapes. We have now. See Contiguity for details on how various states are handled.
When 2020 Data Becomes Available
As noted in the Convert dialog text above, once the official 2020 census data are available for a state, maps using the “Latest Total Population” and “Latest Voting Age Pop” datasets will automatically pick it up.
Features Only Available For 2020 Maps
Finally, there’s one major feature that will only be available for maps using 2020 shapes: painting with blocks. Using that feature, you’ll be able to assign individual blocks to districts and get district populations almost exactly equal.
