map.setCenter(new google.maps.LatLng(37.4419, -122.1419), 13);
The setCenter JavaScript method takes in the center coordinate and a zoom level. The zoom level, as you might expect, determines how far the map should zoom in. The zoom level ranges from 0 (all the way zoomed out) to some upper value (all the way zoomed in). The max zoom level for a particular area depends on the location (for instance, you can’t zoom in too far on North Korea) and the map type (default, satellite, hybrid, terrain, etc). Typically, the max zoom level for an area is somewhere between 15 – 21.
For openstreetmap, we can refer to http://wiki.openstreetmap.org/wiki/Zoom_levels