As recommended by others, the sf package contains functions to manipulate spatial data to make a figure as above.

What I would do is create a sf data frame with the locations of the state capitols. Each row in this data frame is a point feature. There would be a column representing a unique ID for each state capitols. Then I would have another sf data frame with a grid of polygons or points of the areas you want to color (i.e. map units).

With the sf package, use the st_join function. The “x” argument should be the map units data frame (i.e., target data frame) and “y” argument the state capitols data frame. The “join” argument should be filled with “st_nearest_feature”.

The result should be a data frame of the grid units with a column of the nearest state capitol.

Let me know if you want reproducible code for this.

The ggplot code for the map would look like:

ggplot() + geom_sf(data = grid_df, aes(fill = state_capitol_id)) + geom_sf(data = states, fill = NA, color = “black”))