Moving Alaska and Hawaii for Mapping in National Maps

Problems Mapping Alaska and Hawaii

As anyone who has tried to make a map of the United States would tell you, the true locations of Alaska and Hawaii make creating good national maps difficult. Including these two states in their true locations leaves a lot of blank space on the map. As such, maps will oftentimes either cut out Alaska and Hawaii and only show the continental United States or resize and move them so as they appear close to the other states. The latter option is definitely preferable if you want to include Alaska and Hawaii in your map.

Scaling and Translating Alaska and Hawaii

Scaling changes the size of a geometry and translating it moves left, right, up or down. Given Alaska’s size, particularly in coordinate reference systems like 3857, Alaska and Hawaii need to be scaled and translated to fit in nicely with the lower 48 states. One quirk with scaling geographic data is that if you are attempting to plot sub-state geographies of Alaska and Hawaii, the scaling step may pull these geographies apart, as in the example below:

In the above map, the counties in Alaska and Hawaii being plotted are not scaled around a fixed point, but instead to the center of their own respective geometries. This is mostly fine for Hawaii as its counties largely consist of islands, but destroys the county adjacency relationship in Alaska. If you scale the county geometries around a fixed point however, the adjacency relationships are maintained and Alaska looks just like you’d expect it to, as in the map below:

Code to Scale and Translate Alaska and Hawaii

I’ve had to perform this operation many times and have found myself digging back into old code to find the exact numbers used in the scaling and translation. The code below includes the necessary scaling and translation to move data for Alaska and Hawaii in a Python GeoDataFrame to these locations.

The fourth parameter used when performing the scale operation is the fixed point. Please note that the code currently modifies the GeoDataFrame to be in crs 3857. For other coordinate reference systems, different scaling and translating values may be required.

The code takes in a GeoDataFrame containing data for Alaska and Hawaii, a string to refer to the column name where Alaska and Hawaii can be filtered and then inputs for the values for Alaska and Hawaii in that column.

def move_alaska_hawaii(gdf, filter_col, ak_id, hi_id):
    
    gdf = gdf.to_crs(3857)
        
    alaska = gdf[gdf[filter_col] == ak_id]
    hawaii = gdf[gdf[filter_col] == hi_id]
    
    remaining = gdf[~gdf[filter_col].isin([ak_id, hi_id])]
    
    alaska = alaska.set_geometry(alaska.scale(.2,.2,.2,(-13452629.057,3227683.786)).translate(.215e7, -1.36e6))
    hawaii = hawaii.set_geometry(hawaii.scale(1.5,1.5,1.5,(-14384434.819, 2342560.248)).translate(.57e7, 1e6))
    
    gdf = gp.GeoDataFrame(pd.concat([alaska, hawaii, remaining]), crs = 3857)
        
    return gdf