I am trying to convert some polyline coastline data into a polygon that I can use to clip/subset back other data sets by this polygon. There are some small gaps in the coastline data, which FeatureToPolygon struggles to get just how I want it. Any advice?
try the tool Split Polygons With Lines. At first you have to create a polygon which covers the whole area. Then use the tool. After using the tool you can easily delete the parts which doesn't matter to you.