Resolution is the amount of pixels a screen can display. For example, a screen resolution of 1280x1024 would be 1280 horizontal bars of pixels, each 1024 pixels tall. Getting the right resolution setting in a game will make it look better and in some cases improve performance.
In SimCity 4Edit
To set your preferred resolution, navigate to the in-game Options menu and select "Graphic Options" in the menu that appears. The Graphic Options window will show, allowing you to select a resolution to use. The possible settings are: 800x600, 1024x768, 1280x1024, and 1600x1200. Once you choose a resolution, press "Accept" and restart the game for the changes to go into effect. If your screen's resolution isn't listed in the window, read the guide on setting a custom resolution below.
SimCity 4 supports the use of custom resolutions. The current supported resolutions are: 1280x800, 1440x900, 1680x1050, 1920x1200, 1360x768, 1024x600, 1600x900, 1920x1080, and 2048x1152. To set a custom resolution in SimCity 4, you need to change the target of your SimCity 4 shortcut. To do this, right click the shortcut and select Properties. In the properties window, add this to the end of the "target" text box: -CustomResolution:enabled -r1366x768x32, changing the "1366x768x32" part to the specifics of your screen (e.g. WIDTHxHEIGHTx32BITor16BIT). Your target should look something like: "C:\Program Files (x86)\Maxis\SimCity 4 Deluxe\Apps\SimCity 4.exe" -CustomResolution:enabled -r1366x768x32, the path changing according to where you have installed SimCity 4.
If you're running Sim city 4 from Steam, you can do the following to set a custom resolution. Right click Sim City 4 in your steam libary and choose properties. Next click "Set launch options...". In this field you can simply insert -CustomResolution:enabled -r1366x768x32, changing the "1366x768x32" part to the specifics of your screen (see above).