Sorry! I thought it was fairly clear that I meant positional in the layout sense rather than positional in the inter-element relational sense.

I have no idea whether the OP's data is tabular in nature, but he did mention a "2D grid of little circles" which may mean that there is some row-wise and column-wise relationship between the the circles, which I would take to be a tabular nature? Alternatively, it could be that they are simply an un-ordered collection or even a series that is too messy to present using a natural flow type of layout and too long and thin as a single dimensional table, whether horizontal or vertical. I can guess at various other purposes behind the 200 to 500 small circles, but I didn't know.

One application I have used small coloured circles for is to represent the status (red/amber/green) of various resources. In my case, with only 3 actual png's involved, although they were re-used several dozen times each, only three hits were made to the server for a page refresh as the browser satisfied the second and subsequent requests from is cache.

We used css to position them relative to the name (actually a link) of each resource. The links themselves where positioned in a table, although there was no particular row-wise or column-wise relationship, as it was the most versatile and compact way of presenting a large volume of data on the limited set of browsers we had to cater to in our intranet environment.