Hello everyone! I've recently became a Dungeon Master, and while the roleplay part is going well - I'd like to improve my mapmaking skills for Roll20. I've currently made a "prototype" map for a main city of my campaign called Arrowfield: a city situated on a tributary.
I would like to preface that I am not particularly attached to almost anything about this map, and anything may be changed - all advice is heartily welcomed.

Attachment 72428

I understand the small size issue, and when I redo the map it will be at 300ppi. Technically, I tried a fusion of pen-tooling individual buildings and applying district "patterns" over those buildings. How do they work? I don't have the time to manually create realistic buildings, but would like to progress to it. I'm not fond of the background texture (is there any advice for finding more subtle textures?) or the road system. I understood the concept of a developing city but would love it if it could be elaborated upon. How does the elevation mapping at Crow Hill, Bowyer Castle, and the Theatre District work? I personally feel, right now that it's a bit too subtle. I'd also like to go more into detailed mapping after I expand the image.

And there's a catch, or rather, an explanation.

This is not the city I'm actually building currently, it's the city a decade in the past. Over that decade, an aboleth (underwater murky before-the-Gods aberration / mini-Cthulu) shifted into reality in a subterranean lake in Crow Hill. This slowly poisoned the water supply, rapidly dried up and collapsed the mines, and has brought a blight to all downstream crops. Also, annually, there is a free-for-all among the feudal lords of the country of Arrowfield (akin to the Purge) as they vie for power and adventurers attempt to claim a noble title, this presents a stable annual risk to Arrowhail. That is why I decided to restrain Arrowfield primarily to the tributary's peninsula.

Now, with that in mind, how does the city change - is my question. It's really what would be the most interesting. An expansion or renovation of the slums into previous mansions? A shift of major goods of to the Easterly river? Et cetera, et cetera.

So, in sum, my questions are:
How do the technical aspects (pen-tooled, pattern overlaid buildings / background texture / elevation mapping) work?
How would magical-pollution and annual periods of war affect the already developed city?
And, now that I think about it, would you do the map in overall grittier fashion with this development?

Attached is the .psd, if you would like to fiddle with it!
Thank you for your time.