gsymblib contributors (sorted alphabetically)

Daven Quinn
- Maintains the FGDC SVG patterns repository from where we pick the patterns.
Erika Luzzi
- Symbols contribution
Luca Penasa
- Code contribution for the generation of the reference symbols table
Marc Hunter
- Symbols contribution
Valentina Galluzzi
- Symbols contribution
All the people contributing with comments and suggestion in the issue page