International Cellphone Network Coverage Map/API

Query:

I am trying to find a map, or database/API, which shows the cellphone network coverage given an arbitrary point for anywhere on the planet.

This is in the context of planning a hypothetical around-the-world voyage, so coastal coverage is of primary interest, but the generalized form of this question is for any point on earth's surface, land or sea. The path planning for this notional voyage will optimize for staying close to coasts where there is at least 3G coverage, and attempt to reduce the length of non-coverage legs.

The more essential assumption in this question is that a typical international roaming data plan will be compatible with all the coastal networks found in this search*. A more broad follow-up question would be: What is the current state-of-the-art for international roaming cellphone data plans? Which vendors allow for world travel with a single plan and no SIM card switching? Ideally, I do not want to reconfigure the around-the-world cellphone with location-specific SIM cards or other trauma.

The correct answer for this question would answer the following programmatically, or with light human-user interaction:

What are the cell networks, if any, that cover 26.186,-80.086? 7.350,-12.405? -8.447,112.659?
For each network, what is the link type? 3G? LTE?

Own Search Results:

I've searched using terms such as "global cellphone coverage kml" and variations. Here is what I am finding:

https://www.gsma.com/coverage/ - This is quite possibly the closest solution for my query, but it is only a per-nation and per-carrier presentation. It might be possible to web scrape this source, or perhaps there is a bulk/raw version of the database, or an API, but it is likely this will require membership or payment of some sort?
https://webcoveragemap.rootmetrics.com/en-US - Like the GSMA result, this also allocates results based on what specific carrier is selected in the user interface.
https://www.opensignal.com/networks - Same story. Select the nation, then the carrier. No way to compile all networks for the entire globe, or to select an arbitrary point and resolve coverage offered.