Projected coordinate system buffer producing incorrect buffers using GeoPandas

Question

I am still new to GeoPandas.

The issue I'm running into this time is although I have projected my gdf, the buffers created still are much too large. I've run this with a number of different projections (https://spatialreference.org/ref/?search=california) for Zone 2 and I still wind up with the following output:

Here is my code:

latlon = (points['y'].iloc[0],points['x'].iloc[0])
cnode = ox.get_nearest_node(sacroads, latlon)
subgraph = nx.ego_graph(sacroads, cnode, radius=trip_time, distance="time")
node_points = [Point((data["x"], data["y"])) for node, data in subgraph.nodes(data=True)]
nodes_gdf = gp.GeoDataFrame({"id": list(subgraph.nodes)}, geometry=node_points)
nodes_gdf = nodes_gdf.set_index("id")
edge_lines = []
for n_fr, n_to in subgraph.edges():
    f = nodes_gdf.loc[n_fr].geometry
    t = nodes_gdf.loc[n_to].geometry
    edge_lookup = sacroads.get_edge_data(n_fr, n_to)[0].get("geometry", LineString([f, t]))
    edge_lines.append(edge_lookup)
elines = gp.GeoDataFrame(gp.GeoSeries(edge_lines))
elines.columns = ['geometry']
elines = elines.set_geometry('geometry')
elines = elines.set_crs(epsg=3491)
elines['geometry'] = elines.geometry.buffer(10)

Answer 1

As I mentioned in the comments, your post here is bit difficult to work through; and to me, it's doing what I'm expecting: namely, buffering a point (-120, 40) by 10 results in the appropriately sized Polygon form (-130 to -110, 30 to 50).

However, I think I understand what your confusion is. You're setting the coordinate system here:

elines = elines.set_crs(epsg=3491)

This does nothing to the coordinates! A (longitude, latitude) pair of (-120, 40) simply becomes a xy pair of (-120, 40). You're looking for reprojection instead... which looks almost the same, to be fair:

elines = elines.to_crs(epsg=3491)

Here's a minimum working example on my part:

import geopandas as gpd

gdf = gpd.GeoDataFrame(geometry=gpd.points_from_xy([-110.0], [40.0]))
gdf = gdf.set_crs(epsg=4326)  # Set to WGS84; lat-lon in degrees
reprojected = gdf.to_crs(epsg=3491)  # Reproject; meters
print(reprojected)

This actually results in a reprojected geometry, with different coordinates:

                         geometry
0  POINT (3021794.294 826586.522)

Answer 2

In the next-to-last line of your code you use "set_crs" which tells the dataset it is in some crs; it doesn't actually transform the data. To do that, you need to use "to_crs".

I have no idea if the rest of your code is right as you don't provide the context.