Is there any way to define a map boundary other than with the square/rectangle tool? It would be really helpful if you could define your area using a polygon. I'm trying to estimate sediment deposits through a channel system and need to exclude some areas but cant using the rectangle tool.

You may need to get creative with map boundaries (shorelines and islands). These do not have to represent actual shorelines, and can instead be used to define the edges of your mapped area. The key thing to remember is that nothing outside of a "shoreline" is generated, and nothing inside an "island". If you do use boundaries in this way, then you will probably want to uncheck the option "provides depth". This option is normally used to add data of a specific depth (usually zero) which is used during map generation. When the option is un-checked, the boundary acts only as boundary and not as a depth data source.

That's perfect. I didn't realize you could do that. Thanks Matt.