How to compute outline of geometry from union of geometries

Question

How can I compute the outline corresponding to the union of a set of geometries? Specifically, given geometry of 50 states, I want the outline of the contiguous continental US.

Using gz_2010_us_040_00_5m.json from https://github.com/kjhealy/us-county/tree/master/data/geojson

import geopandas as gpd
import numpy as np

country = gpd.read_file("data/gz_2010_us_040_00_5m.json")
conus = country[country['NAME'].isin(['Alaska','Hawaii', 'Puerto Rico']) == False]

Now we have the outlines for each state. How can we join this into the outline of conus?

Answer 1

Here's what I ended up doing. First, I added a column 'country' to all the states, then used 'dissolve (by='country'):

conus.loc[:,'country'] = 'usa'  # produces warning, don't know how to avoid
us = conus.dissolve(by='country', aggfunc = 'sum')