Some simple, frequently used functions for creating a map with D3.js and Topojson.
centerZoom- Automatically centers and scales your map to its container, and returns your map's outer boundaries in case you want to draw them.drawOuterBoundary- Uses the boundary returned fromcenterZoomto draw a boundary around your whole map.drawPlaces- Draws place names, if your topojson has places.drawSubunits- Draws subunits.
See this tutorial for more on making maps with D3. I got most of the centerZoom function from this block.