how to send spaces in the url

I need to send an array like: $layers = {"airport runways", "buildings", "census blocks", "national rivers"} to a new page in the url. I understand that a space is encoded as "&" but that will also be understood as the beginning of another vari. Right now I have names with "_"s. http://titan.erc.msstate.edu:8080/mcrgdl/changeLayersDrawOrder.html?layer[]=aban_railroads&layer[]=airport_runways2001&layer[]=blk_grps&layer[]=buildings2&from=http://titan.erc.msstate.edu:8080/mcrgdl/test.php Are there any directly available functions in php to do this, I looked at htmlentities() and some other but don't think this is the answer. Thanks, -Pushkar S. Pradhan