Dharmawiki:WikiProject Geographical coordinates/scale:

The scale: parameter specifies the desired map scale as 1:N, overriding the scale implied by any type: parameter.

GeoHack uses scale: to select a map scale for a 72 dpi computer monitor. If no dim:, type:, or scale: parameters are provided, GeoHack uses its default scale of 1:300,000.

Samples

Subject	Scale	Markup	Result
Big Ben	1:500	{{coord|51.500611|N|0.124611|W|scale:500}}
Palace of Westminster	1:5,000	{{coord|51.5006|N|0.1246|W|scale:5000}}
City of Westminster	1:50,000	{{coord|51.501|N|0.125|W|scale:50000}}
Greater London	1:500,000	{{coord|51.50|N|0.12|W|scale:500000}}