You can try the Ushahidi approach
We built the Ushahidi platform as a tool to easily crowdsource
information using multiple channels, including SMS, email, Twitter and
People can submit reports by:
- Going to the web page
- Sending an SMS
- Using the Android app
It was originally intended as a tool for monitoring election related violence and suspicious activities. It has since been used in Haiti and other disasters.
Here's an example of an Ushahidi deployment
You should be able to adapt it to your purposes. Ushahidi only deals with point data though. If you need to deal with lines and polygons, you're out of luck.
Another option would be Localwiki.
It's a tool for collaborating in local, geographic communities. It has integrated support for mapping. Your users can delineate an area or trace a line on the map and then write what they know about it on a wiki page.
Every feature of a local wiki involves a place: where news events
happen, where sites are found, where neighborhood boundaries are, and
how to get from point A to point B.