Thanks for your help
1) By giving BoundingBox method I got some selected area.
Dim box As New SharpMap.Geometries.BoundingBox(76, -16, 100, 24)
But after ZoomIn, I have to Zoom only the selected area. But its zooming all map area
2) I have to get grid lines on entire map and each box may shown as 30 miles of distance
Please help me