The Shift layer shows how differently 100K districts turned out from 2020 to 2024, 2016 to 2020, and 2016 to 2024 (all elections in the Trump-era). Red means more Republican, blue means more Democratic, and white is relatively unchanged. The tooltips also have the exact shifts, in addition to 2016, 2020 and 2024 results in each district.
If you want to change the layer, just use the tooltip in the top right of the map. As with every 2024 map, no California or Maine as of 4/18/25.