instaviz: URL's always use an "inner" URL that expresses the graph you want to display, for now Instaviz understands data: , http: and https: inner URL's.

Application homepage:
iTunes link:
HTML Link example: <a href="instaviz:data:,digraph G { hello -> world; }">Graph it</a>
Native application URL string example: instaviz:
Extended example: instaviz:data:;base64,ZGlncmFwaCBHIHsgaGVsbG?8gLT4gd29ybGQ7IH0K

Use the DOT language to draw up graphs and let Instaviz draw them.
Please refer to the The DOT Language webite for more info.