@Burning Full Fingers Okay let me try to elaborate
"Altering the world map" can be as good as removing a specific huge terrain that used to be on the spot. Say for this case, Trihexa was wiping out forests, lakes, and mountains through it's fire breath. In the aftermath, said forests, lakes, and mountains that's supposed to be there were gone and became a barren land or some of the mountains' shapes were altered from the blast depending on how much was affected. The "altering the world map" part here would be that the forests, lakes, and mountains were not there anymore like it used to be and it's just going to be something like a barren land or may have some mountains that have different shapes due to how affected it was. It doesn't necessarily mean that it have to go on a country scale for it to be considered as " altering the world map." Even taking out portion of the mountain range can be considered as "altering the world map."
Also, completely wiping out an island can be considered as "altering the world map" due to how it's basically removing a geographical landscape that supposed to be there for the current world map.
There's also the problem about Trihexa's location where it was destroying forests, lakes, and mountains as well so we cannot easily assume that it's actually trying to destroy bigger mountain ranges that's only located on specific parts of Europe.
Check this map for elevations in Europe.
Besides, destroying forests, lakes, and mountains at the same time is already big as it is to warrant "altering the world map" description.
We also have to take into account that Ishibumi could be dramatizing what's going on on top of not giving us a good clue about it's size.
This same goes for the Loki statement in regards to "carve and repaint the world map" when shaving a chunk of land in a country is already considered as changing the geographical landscape, which what "carve and repaint the world map" may meant due to how the shape of the coastal area of the country may be changed if the shot was successful.
At the moment, for a single head of Trihexa, maybe he can at least be powerscaled to True DxD Issei at least since it was used to be powerscaled before the recent tier changes (aka
at least Low 6-B likely higher). For full powered god tiers, Unknown would still be the safest bet.
In regards to country level maous, was this based on Serafall statement again? Wasn't it also rejected before due to how it's unknown what glittering may entailed?