For an interactive map check out Google Maps. You can also see a single 3mi swim loop (Grimaldo's Chair to the White Building, then to the Coney Island Pier, then back to Grimaldo's Chair) with this Gmap Pedometer Course. Here are some swim distances, parallel to the shoreline approximately 100yds out, past the jetties - care of Tom McGann.

From To Yards Meters
Grimaldo's Chair Small rocks (West of Grimaldo) 416 382
Grimaldo's Chair Large rocks (West of Grimaldo) 619 566
Grimaldo's Chair Ex-White Building (Now Red) 824 753
Grimaldo's Chair Cyclone 1,480 1,287
Grimaldo's Chair Coney Island Pier 1,956 1,789
White Building Coney Island Pier 2,779 2,541
Coney Island Pier Seagate 1,703 1,557
West 22nd St. Next set of rocks (either direction) 200 183
West 22nd St. Coney Island Pier 503 460
Ex-White Building (Now Red) Seagate 4,482 4,098
Rocks (East of Grimaldo) Small Rocks (West of Grimaldo) 776 710
Rocks (East of Grimaldo) Large Rocks (West of Grimaldo) 959 877
Ex-White Building (Now Red) Large Rocks (West of Grimaldo) 1,443 1,319