What are you trying to do?

Here is the link to the sdk

http://world.episerver.com/documentation/Class-library/?documentId=cms/9/33DCC733

IUrlSegmentRouter segmentRouter;
            ServiceLocator.Current.TryGetExistingInstance(out segmentRouter);

            if (segmentRouter == null)
            {
                return;
            }

            segmentRouter.RootResolver = sd => sd.StartPage;
            var parameters = new MapContentRouteParameters
            {
                UrlSegmentRouter = segmentRouter,
                BasePathResolver = RouteCollectionExtensions.ResolveBasePath,
                Direction = SupportedDirection.Both
            };

and here im getting this error

It referrs to EPiServer.Web.Routing.BasePathResolver

Depending on the context of your code you can get either as a constructor dependency (if your class instance is created from IOC container), else you can get it from ServiceLocator.Current.GetInstance<BasePathResolver>()