I want to generate the shortest distance to coastlines from interested points worldwide. My question is given existing world map polygon file, what the standard way to create coastlines is. Thanks very much!
You could dissolve all polygons together to create one big landmass. Then, convert to polylines using the Feature to Line tool. Note, Feature to Line requires an ArcGIS for Desktop Advanced license. However, there are other tools out there that will convert polygons to polylines.
XTools, for example.