F7 for node mode: then ctrl-space to add a new node, then 'N' over node to change the node type (ie, current 2 500) then space to add a node path. I'm at work right now so I don't particularly remember what key it was off hand, but I believe it was Y to change the type of Node from Square to Circle shape. The node area can also be expanded just like the controls to modify tiles in the tile editing mode.
As far as getting past the original circle, you have to make your own map with a paint program and use white (RGB 0,0,0) for the areas that naija is to swim in, and black (RGB 255, 255, 255) for the solid areas. It helps to have your own mod folder. Whatever you want the mods name to be, in a subfolder of _mods. There should be plenty of information on how to do this here in the forums. Use the search feature and I guarantee you will find the information you need here.
