It would look very unique to have different categories and emblems added to town description and dynmap respectively.
In the same way a nation's capital is displayed by a Temple emblem, I believe each town category should have it's own distinct emblem such as:
Naval port - Anchor
Industrial town - Cog and wheel
Military base - Soldier helm
Fortress / Stronghold - Castle tower
Merchant town - Coins
Town (advanced) - Skyscraper
Town (undeveloped) - Standard house
etc.
Implementing emblems highlights the unique role each town plays within a nation on the dynmap. I think a lot of people would love to see this suggestion implemented if possible due to increased nation building roleplay & immersion.
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Side notes:
Only high ranked nation officials are able to appoint town categories, this incentivizes mayors to develop their town for an emblem to be bestowed upon them. It also increases the accuracy of each town's category as nation leaders strive for a higher quality control.
I am aware that the current towny plugin has town categories such as Hamlet, Village, Metropolis but those are dull and do not reflect a town's role within the nation at all. I do not believe they should be removed however, they can compliment the new system I proposed.