The ShapeFile provider is used for accessing ESRI ShapeFiles. The ShapeFile should at least contain the [filename].shp, [filename].idx, and if feature-data is to be used, also [filename].dbf file.
The first time the ShapeFile is accessed, SharpMap will automatically create a spatial index of the shp-file, and save it as [filename].shp.sidx. If you change or update the contents of the .shp file, delete the .sidx file to force SharpMap to rebuilt it. In web applications, the index will automatically be cached to memory for faster access, so to reload the index, you will need to restart the web application as well.
M and Z values in a shapefile is ignored by SharpMap.