I needed to install graphviz to generate diagrams using the SchemaSpy tool with my database. When it runs dot it encounters the following error: dot -Tpng:gd /tmp/mmschema/diagrams/summary/relationships.real.compact.dot -o/tmp/mmschema/diagrams/summary/relationships.real.compact.png -Tcmapx: Error: fontconfig: Didn't find expected font family. Perhaps URW Type 1 fonts need installing? Once I installed the x11-fonts/urwfonts package, these warnings went away, and it was able to generate the diagrams instead of failing to generate any image. It seems to me that this font package should be a dependency of graphviz.
I think this is really an issue with the schemaspy software requesting a font name "Helvetica" which is otherwise not found in the fonts used by many other programs (not in webfonts, or the xorg type1 fonts collections) which I had installed already. Feel free to ignore this. Sorry for the noise.
The fonts are defined in the dot files. The software defining the font names should require the needed font.