27d7da41_mGeoJSON___University_Map_Wiki__lines
[property name] stroke-opacity [filled shapes] the opacity of outline [notes] a number between zero and one e.g. 0.5. If not given, opacity is used in both cases (so if you just give opacity it applies to both the filled shape and its outline). [lines] 
the opacity of the line
UCamGeoJSON - University Map Wiki
lines