The solution is set map unit equal meter.
And assign projection to the shape file layer convert it from epsg 4326(WGS 84) to 3857.
The code should looks like:
Proj4Projection proj4 = new Proj4Projection(4326, 3857);
ShapeFileFeatureLayer layer = new ShapeFileFeatureLayer("Your Shape File");
layer.FeatureSource.Projection = proj4;
Our V10 API should be different than V2, you can learn more about them in our wiki.thinkgeo.com, or you can view our sample in https://github.com/thinkgeo
Wish that's helpful.