I don't understand what it means when Tiles are "Worked"

[spilo]

Do the green Worked tiles mean those are the only tiles in the surrounding area being utilized in any possible way? Implying that all the other non-worked zones are empty dead space, even if they have Improvements on them?

Does this mean its pointless to Improve ALL tiles in a city's area, since only a small number can actually be worked?

Also in the screenshot, 3 tiles from the city's tile are highlighted. But the city's "zone" seems to extend 5 tiles out. Are the darkened tiles along the periphery deadspace, whose only possible use would be to differentiate hostile territory for enemy military units?

 

[Browd]

View attachment 461546

Do the green Worked tiles mean those are the only tiles in the surrounding area being utilized in any possible way? Implying that all the other non-worked zones are empty dead space, even if they have Improvements on them?

Yes

Does this mean its pointless to Improve ALL tiles in a city's area, since only a small number can actually be worked?

Unless you expect the city's population to grow substantially, there may be no need to improve all tiles in range. Some tiles will always be improved, to obtain the luxury or strategic resources on those tiles, even if you don't plan to work those tiles. It can be useful to improve other tiles because you don't want your citizens to work tiles that are not improved (improvements add to tile yields). over the course of the game, your priorities/needs for a city may change (e.g., growth, or production, or science, or gold), so having a suitably wide range of improved tiles allows you to reassign citizens on the fly, without having to worry about rushing down a worker to improve a tile that you now decide you want to work.

Also in the screenshot, 3 tiles from the city's tile are highlighted. But the city's "zone" seems to extend 5 tiles out. Are the darkened tiles along the periphery deadspace, whose only possible use would be to differentiate hostile territory for enemy military units?

That is the case -- you can only assign citizens to work tiles in the first 3 rings of tiles around the city center, but your culture borders can extend out to 5 tiles, allowing you to obtain luxury and strategic resources from those tiles and to extend the territory in which your units will enjoy "friendly" territory benefits (including accelerated healing) and to push enemy units further away if they choose to start a war.