I like your analogy better. But it still implies that you could feel one car and one house, which you couldn't.

So, perhaps an even better analogy would be:

If the Earth was the size of an orange, your finger could feel the difference between cities and forests.

This puts more emphasis on the distinct patterns the objects form as a group, rather than the individual objects.

That still requires a pretty impressive feel for the relative size of oranges and planets though. I would have preferred something like this table:

  2 nm Diameter of a DNA Alpha helix

  4 nm Globular Protein

  6 nm microfilaments

  7 nm thickness cell membranes

 20 nm Ribosome

 25 nm Microtubule

 30 nm Small virus (Picornaviruses)

 30 nm Rhinoviruses

 50 nm Nuclear pore

 100 nm HIV

So 13 nm is on the scale of a very small virus... :)

A virus is 30nm? Good lord. The minimum feature size of commercial transistors is half that right now.

Something tells me that you don't really need an analogy at all :)