A control city is a city, locality, or other location posted on a series of traffic signs along a particular stretch of road indicating destinations on that route. Together with route numbers and cardinal directions, these focal points aid the motorist navigating along a highway system. Such cities appear on signs at junctions to indicate where the intersecting road goes and where the road ahead goes. They are also typically used on distance signs.

Different countries have different practices as far as focal points on directional signs are concerned, and the term control city is not used globally. Where a sign contains a number of destinations for a particular direction, not all of those destinations may be considered a control city. In most countries, control cities are perceived to be the destinations on signs that aid longer-distance traffic, as opposed to local traffic. Accordingly, local destinations on a sign, which only appear incidentally, would in a number of countries not be considered control cities.

While a control city may not appear on the signs of every single junction, the control city would at least appear on major junctions.

Mostly towns and cities are used as control cities. Other than major towns in a country or region, towns close to major intersections or the end of a particular route are often selected as control city. However, all sorts of other potential destinations can be selected as control city, such as states and regions, frequently visited objects, and names of prominent intersecting roads. Narrow-passes carrying a lot of traffic often also take the role of control city. Examples would be major bridges (the Golden Gate Bridge is a control city within San Francisco), tunnels (e.g. the Holland Tunnel in New York City), or mountain passes (e.g. the Gotthard Pass featuring prominently on signs in Switzerland). In border areas, the border itself regularly features as a control city, e.g. the U.S.-Mexico border for Interstate 5 southbound.

The control city is typically on or close to the route for which it serves as the primary focal point. In exceptional situations, towns along prominent intersecting roads could serve as such, notably when the vast majority of traffic would turn off to that intersecting road. Equally, towns beyond a route's terminus could serve as control city. Particularly when a route merges into another route, a major town along that other route could serve as control city. In the United States, for instance, New Jersey Route 18 southbound says it goes to Point Pleasant but never does. This is because of the stub end at exit 6.

While the vast majority of control cities are sizeable towns, minor towns or even unincorporated localities may feature as control city. This is particularly the case if they are located close to junctions of major roads or near the terminus of a road. Major roads in Poland, for instance, feature many signs that refer to small villages close to the border, since that border marks the route's terminus. Signs in Australia's Northern Territory generally will not refer beyond the state border, with the last control city on the Stuart Highway being SA Border and the same applying on routes heading to Queensland and South Australia. On the other hand, there are also instances where larger cities have not been selected as control city because of the proximity of a bigger city downstream on the road.

A common principle identified in signposting is the principle of continuity. Once a particular destination has featured on a sign, it should feature on all signs that contain forward destinations for that direction. Sometimes particular towns are used on a one-off basis at major intersections, but they would then not be considered the control city for that particular road.

Unlike in the United States, Canada, and the United Kingdom, roads in Continental Europe are not signed with directional banners (east, west, north, and south). The motorist accordingly needs to rely on the combination of the control city and the route number as navigation tools. Possibly as a result of this, control cities tend to feature rather prominently on the route signs of European countries when compared to signage in North America. Routes tend to feature more signs that contain information for the route forward and those signs often contain a larger number of focal points.