What to do with workers in Civilization 5 when all tiles improved?

First of all, you can just sell them if you don't need them. Not only do you immediately get some gold, you also decrease the number of units you own, and units cost gold each turn.

Secondly, connecting a city to the capital by railroads greatly increases a city's production, so if you can afford it it's recommended.

Finally, you can replace improvements you don't need / want with other improvements. For instance, for cities that are big enough it's probably better to replace farms with mines or trading posts.

You can set your workers to "automate", and they will automatically build roads, replace them with railroads if available, and will replace improvements with other improvements the AI thinks you need more.

Possible, but normal, things you could do with workers, when they are not active:

• Delete them, to save on maintenance.
• Gift them to city-states, for (minor) influence.*
• Gift them to other civilizations, for (minor) influence.*
• Use them to build roads inside an "allied" civilization's borders, for fun and profit.
• Use them to watch otherwise unwatched hexes, to prevent barbarian camps from spawning.

*Edit: workers can not be gifted because they are not combat units.

The first few options are better in the late game when you're workers are done for good. However, if you're running out of things for your workers to do so fast, your probably have more workers than you need anyway.

I think Civ 5 is very well balanced regarding worker employment situation. As a general rule I have one worker per city, that taking I don't have any worker speed increasing wonders or policies.

It's actually very simple and at the same time clever - just follow the natural city expantion rules.

When you just build your new city the emphasis is on expantion so you build farms and a mine or two in surounding one tile territory. Well you want to get available resourses and therefore buy some land, but that is obvious, so I'll just ignore it here. When your city starts to expand to the two tiles ring you build more farms and mines. And probably thats about time to connect your biggest cities by road (which is also very usefull for waging war).

But what about trading posts, you ask. Actually I don't find them necessary in the early game as the economy is running pretty well using gold from resourse tiles. I don't usualy find a city if it doesn't have at least 3-4 resourse tiles nearby in the first place. But by all means be flexible - if you have to wage a war and need some cash build some trading posts.

Ok, now your city is pretty big and it takes the third ring of tiles out. Guess what, you build more farms there :). But at the same time you start to build trading posts next to your city. That's right NEXT to your city, where previously farms used to be. And that is a natural thing - those trading posts don't just pop out from nowhere - your city is expanding.

And now zoom out and look at your map. It's beutifull. The tall buildings in the centre of the cities, surrounded by smaller suburbs (trading posts), the huge lands of farms in between. Now campare it to the mess generated by AI workers...

Basically where are three reasons to follow the natural city expantion path:

• you don't have to buy land (except of some resource tiles) and can save cash for something else as natural culture expantion is enough,
• your workers are kept busy pretty much till the end of the game,
• your map looks fantastic.