[R-sig-Geo] Is there any function to create buffer zones

[Xin LIN]

Hi list,

Is there any function to create buffer zones for polygons? For example, here
I have polygon shapefile of a city. I want to create a buffer zone 1km
outside its boundary, or a buffer zone with its area equal to that of the
city. Then which function should I use here? 

Any suggestion is welcome. Thank you so much for your help.

Best,

Xin