Massive improvement to borders and how they are played.
1. Crossing a border and invading someone else's territory should be considered an AN ACT OF WAR. Not simply a transgression that you get annoyed at, but they get away with.
2. Units should bring a small "culture zone" with them.. much like the square you get moving a settler around.. except it's a real colored border, and you can draw food from it, ask enemies to leave it, etc. It is essentially "controlled territory".
This would correctly represents the control and impact units and armies have upon uncontrolled/unclaimed territory. If units are near your cultural borders, your border stretches and meshes with their control. The "culture zone" is equivalent to the number of moves per turn a unit has, but also obeys "culture clash" rules, as if you'd built a city next to someone else's culture border, you know what I mean?
This means you would no longer have outposts. You'd simply move a military unit to the resource. The military unit would exert control on the resource square and surrounding squares - exactly like a military force really does! From this little island of "culture and control" you would automatically draw resources as if it were really within your borders, provided there was a road to take the resources to a city.
In enemy territory, well, imagine building a city in enemy territory and how big the cultural borders of that new town would be.. ie, pushed in from all sides, none at all. A unit's "cultural influence" would be limited to ONLY the square it occupied. This still has significance, however, because if you then land troops in enemy controlled territory and occupy crucial squares, you deny them resources, and more importantly, can take stuff like airfields and claim them as yours without having to take the nearby city.
You could also use units - patrolling just outside your city's cultural limit - to extend your empire's influence and borders. Just like real life. You wouldn't have to man the border with 3902424 units to present a hard physical barrier to enemy civ's who want to plant their city in that obscure "my borders haven't expanded to claim it yet" corner of your continent.
It would also add value to units with more movement, who would exert a larger area of culture and control and be able to push your boundaries even further.
I'd also like to see less cities and more stuff like outposts, adding a greater importance to taking and holding resources and roads. To that end:
3. Roads and railroads should offer no bonus individually and only upon connection with another city (yours or other civ's). When a city is connected to another via road or railroad, ALL squares in that city's radius gain the bonus imparted by the underlying connection medium. Ie, if 5/6th of the connection is rail, and 1/6th is road, the connection bonus is the one imparted by ROAD until the rail route is complete!
Also, rail should not override road, but the two should complement one another. Each city gains a bonus from EACH city it is connected to. Therefore, central "hubs" of travel, with road and rail connections to a myriad of other cities, gain enormous trade bonuses - just like real life! Going to war should affect your border cities the most which are hit economically because their connection to cities that are now their enemy no longer grant a cross-border trade bonus!
Primarily, I want to get rid of the horribly messy "road/rail/irrigate in every single square" ethos that absolutely plagues the game. I'd love my civs to be neat, with one major arterial road and railway going places. I mean.. we don't see the individual buildings in a city unless we zoom in.. so why should we see all the sprawling suburban roads and dead end railroad tracks? Let's pull back from the road/rail spaghetti too.
What y'all think so far?