Simplifying networks

In this example we show how to perform topological simplification on a network.

This process changes the data in place, so we recommend working on a copy of your model, as done below.

import shutil
from pathlib import Path

import folium

from polaris import Polaris
from polaris.utils.testing.temp_model import TempModel

sphinx_gallery_thumbnail_path = ‘../../examples/editing_models/simplification.gif’

original_model = TempModel("Grid")
target = original_model.parent / "simplified_grid"

shutil.copytree(original_model, target, dirs_exist_ok=True)

PosixPath('/tmp/polaris_studio_testing/simplified_grid')

A little function to plot the network, which we will use a few times

def make_map(network):
    network.tables.refresh_cache()
    links = network.tables.get("Link")
    nodes = network.tables.get("Node")

    map = links.explore(color="black", style_kwds={"weight": 1}, tool_tip="link_type", name="links")
    map = nodes.explore(m=map, color="red", style_kwds={"radius": 3, "fillOpacity": 1.0}, name="nodes")
    folium.LayerControl().add_to(map)  # Add a layer control button to our map
    return map

Let’s plot the network we have to begin with

network = Polaris.from_dir(target).network
make_map(network)

2025-10-30 02:28:22 UTC+0000 - No pre-existing parameter file exists for this project. Will use default
2025-10-30 02:28:23 UTC+0000 - Working with file on /tmp/polaris_studio_testing/simplified_grid/Grid-Supply.sqlite

Make this Notebook Trusted to load map: File -> Trust Notebook

Now let’s simplify the network

# Let's allow links to be a maximum of 2000 meters long
# And we will merge links if they have up to 5% difference in speed
# The recommended maximum length is 1,000, but we are using 100,000 here for illustration purposes
network.tools.simplify_network(maximum_allowable_link_length=100_000, max_speed_ratio=1.05, rebuild_network=False)

# What happened to the network after this simplification?
make_map(network)

/home/gitlab-runner/builds/polaris/code/polarislib/polaris/network/tools/network_simplifier.py:28: UserWarning: This will alter your database in place. Make sure you have a backup.
  warnings.warn("This will alter your database in place. Make sure you have a backup.")
2025-10-30 02:28:24 UTC+0000 - Field(s) a_node_network, source has(ve) at least one NaN value. Check your computations
                                                  :   0%|          | 0/15 [00:00<?, ?it/s]
2025-10-30 02:28:24 UTC+0000 - Field(s) a_node_network, source has(ve) at least one NaN value. Check your computations
2025-10-30 02:28:26 UTC+0000 - 459 links will be removed
2025-10-30 02:28:26 UTC+0000 - 149 links will be added
2025-10-30 02:28:27 UTC+0000 - Old distance: 427442.36285424477, new distance: 427442.36285424477. Difference: 0.0
2025-10-30 02:28:27 UTC+0000 - Network has been rebuilt. You should run this tool's rebuild network method

Make this Notebook Trusted to load map: File -> Trust Notebook

We can also delete links and collapse them into nodes For this operation, we just choose an arbitrary link to delete here

network.tools.collapse_links_into_nodes(links=[838], rebuild_network=False)

# What happened to the network after this deletion?
make_map(network)

/home/gitlab-runner/builds/polaris/code/polarislib/polaris/network/tools/network_simplifier.py:28: UserWarning: This will alter your database in place. Make sure you have a backup.
  warnings.warn("This will alter your database in place. Make sure you have a backup.")
2025-10-30 02:28:28 UTC+0000 - 1 links collapsed into nodes

Make this Notebook Trusted to load map: File -> Trust Notebook

Now we can close the network

network.close()