Colorful visual representation of a world map

Coverage Map Now Supports Sharing & Coordinates

I just released a minor update to the coverage map.

  • Sharable map links are now available
  • Users can now enter locations using coordinates (format as decimal degrees; e.g., 38.897700, -77.036500)

The new share options appear in two places. From the main user interface, you can click the share icon to get a link that captures features of your current view (e.g., the map’s center, the color scheme, the selected network and technology). There’s also a share button visible after selecting a specific hex. Links generated with that button direct to a map centered on the selected hex with a pin marking the location.

I’d like to offer my thanks to Reddit user redi20 for the suggestion to add support for coordinates.

Much larger map updates will be coming shortly!

Coverage map of San Francisco

Coverage Map Update – Water & Zooming

I’ve released a new version of the coverage map with a few updates:

  • Restrictions that prevented users from zooming out have been lifted
  • Coverage reporting around bodies of water and shorelines has improved
  • UI changes were introduced for Alaska and US Territories
  • Roads are more visible

The rest of this post is a deep dive into the changes. I’d encourage most readers to skip the post and check out the updated map.

Zoom Freely

Previously, Coverage Critic’s map prevented users from zooming out too far. The zoom restriction is gone now.

With the small hexagons typically used in Coverage Critic’s maps, about 100 million hexagons are needed to cover the US. The map can’t display that many hexagons at once. Rendering breaks when viewing an area much larger than 100 miles across.

The updated map transitions to using larger hexagons when necessary. Roughly 40,000 of these large hexagons are needed to cover the US. Each hexagon is roughly 10 miles across.

Coverage quality is usually heterogeneous within large areas. Portions of a giant hexagon may have great coverage, while other portions of the same hexagon have no coverage. Consequently, the map is colored very simply when users are zoomed out. One color (green by default) is used if at least 50% of a hexagon is covered. If less than half a hexagon is colored, a different color (red by default) is used.

Users assessing coverage will find the most helpful information while zoomed-in and viewing the smallest hexagons available. I’ve designed the map to nudge people accordingly. While zoomed out, users will see an alert encouraging them to zoom in. With the default settings, the color palette changes a bit when large hexagons start rendering. It may not be the most aesthetically appealing design choice, but I hope it gives users an indication that a meaningful transition occurred with the shift to larger hexagons.

I find this approach strikes a good balance with the default map (the one based primarily on FCC data). I’ve not used the same approach for the map that shows crowdsourced coverage data from vehicles. Coverage data won’t render when users of the crowdsourced map zoom out too far. They’ll only see an alert encouraging them to zoom in.1

Better Accounting For Water Hexes

In earlier versions of the map, coverage wasn’t represented consistently around bodies of water and shorelines. I now have a good system for detecting hexes that are fully or partially within bodies of water. However, deciding how to display these hexes within the map is still tricky. Network operators don’t follow the same procedures for determining when and how to exclude bodies of water from their reported coverage areas.

Here’s what the last version of the map looked like when displaying Verizon’s coverage in Miami:

Coverage map screenshot in Miami showing red hexes in a body of water

If you happened to be boating within those red hexes, you’d probably have service. Verizon just excluded that area from its reporting. Most of the problematic hexes don’t appear in the new map, but it’s not perfect. Some stray red hexes occasionally appear on shorelines where coverage actually exists. There are also occasional spots where the map looks spotty because a random hex falling on a river isn’t mapped. Some of the imperfections should be resolved in future versions of the map.

For the sake of scoring cities coverage on a 0-10 scale, the water detection system should function awfully well. I can pretty safely ignore all potential water hexes where networks might be inconsistent in coverage reporting.

Alaska & US Territories UI Changes

With the previous map update, I quietly added data showing coverage in Alaska and US Territories. The map only shows networks’ native coverage, so it may not be useful for users on plans that rely on roaming coverage in these areas. If map users view these areas, they’ll see an alert that cautions them appropriately.

More Visible Roads

I’ve made roads more visible on the map, especially for users that are zoomed-in on small regions. I expect I’ll continue to tweak roads’ display properties over time.

A Work In Progress

As always, I’d love feedback. I want to thank Reddit’s NoContract community for the thoughts they’ve shared so far. Shout out to user Starfox-sf, who had great ideas for this latest update.

Screenshot from Version 2 of Coverage Critic's coverage map

Coverage Map V2 Beta

A beta of version 2 of Coverage Critic’s map is now available.

I’ll discuss the changes in more detail when the map comes out of beta, but the new version includes:

  • A more recent round of data from the FCC
  • Data for two more networks (Dish & US Cellular)
  • New features accessible from the settings menu

Additional features and bug fixes will be added before the map comes out of beta, but I wanted to share something now.

The Coverage Critic Coverage Map

Earlier this year, I quietly released an interactive coverage map that shows the strength of cell signals from the three nationwide networks (Verizon, AT&T, and T-Mobile). I’ve now polished the map to a point where I’m ready to make an official announcement.

If you want to cut to the chase, try the coverage map now. The rest of this post details how the map works, its limitations, and improvements I’ll release going forward.

Map Structure

The information surfaced in Coverage Critic’s map is richer than what’s typically found on carriers’ own maps.

Here’s what the map looks like when representing T-Mobile’s coverage in Vail, Colorado:

Screenshot showing Coverage Critic's coverage map in Vail, CO

Each hexagon is the size of a few city blocks. Darkly shaded hexagons indicate where T-Mobile’s network is predicted to have a strong signal. Lighter shades indicate weaker signals. No coverage is expected in areas in white.

Compare Networks

Map users can toggle between different networks and technologies with a single click.

Screenshot showing menus coverage map users can click on to toggle between networks or technologies.

After selecting a specific hexagon, users are presented with details about coverage within the hexagon:
Coverage map screenshot showing details about coverage in a hexagon
With a few more clicks, users can compare coverage within the hexagon across the major networks:
Screenshot from the coverage map showing details about a hex

Zoom Levels

In rural and remote areas, the map can be informative from a zoomed-out perspective. However, in dense cities, the zoomed-out view becomes chaotic due to a plethora of cellular antennas and tall buildings that block signals.

In big cities, I recommend initially entering an address or the name of a neighborhood. The map will automatically zoom to the selected spot at an appropriate zoom level.

Screenshot of the geocoder users of Coverage Critic's coverage map can use to zoom in on specific areas.

Data Sources

The base data underlying the maps comes from the FCC’s Broadband Data Collection program. I adjust the data from the FCC based on the results of in-house testing.

For the moment, the adjustment procedure is relatively simple, but I have more ambitious plans in the works. In the future, I’ll share more about my in-house testing and my intention to incorporate data from third parties.


The map shows predicted signal strengths rather than on-the-ground measurements of signal strength.

While signal strength is a decent proxy for service quality, it’s imperfect. As the map evolves, I’ll account for additional factors that affect performance.

Known Issues

The map has a few major issues:

  • Coverage data is unavailable in Michigan and Alaska
  • Verizon’s LTE coverage is not correctly represented in portions of the Northeastern United States
  • Coverage information is sometimes missing around bodies of water and state borders

Upcoming Improvements

At the moment, the map draws on FCC data that reflects networks’ coverage as of mid-2022. A newer data set, reflecting coverage at the end of 2022, was released yesterday. As I build a new version of the map incorporating the latest data, I’ll also resolve some of the issues.

Additional networks, including US Cellular and Dish, will be included in an upcoming version of the map.


The map relies on the work of an awful lot of other people. I’d particularly like to thank the FCC’s Broadband Data Task Force, the folks that build and maintain the H3 geospatial indexing system, and contributors to OpenStreetMap.

I’d also like to thank my audience for helping me get this far. I’m enjoying the experience as Coverage Critic evolves into a more useful product.