There are limitless opportunities to create things for your Web site from public information that people will link to. It's all about finding the opportunity, repackaging it to a specific group, and promoting it.
Let's explore how this can be done.
There's a lot of material in the public domain that is free to use to create linkable material. One needs to review copyright laws to find out what is free. This could be photographs, drawings, written content, and even research material. With the right investigation you can even find things that haven't been published online yet. Since you will be the first you are more likely to get the links. Especially if you actively promoted this material.
You must ask yourself, "where can I find this content that isn't online yet?" I would start with older libraries, colleges, government offices, archives, and used book stores. If you approach this from the right angle you may even have a college, or archive, offer assistance to help with your research.
Let's look at the example of using paintings, drawings, and photographs.
Sell music equipment? Publish a graphic history of a specific instrument - showing how it has changed over time with sketches and drawings. A time line would work great here and make it more linkable. I would also create it in a way that educators could use it as a teaching tool in the classroom. That way You are more likely to get links from educational sites.
It's all about finding a unique angle to target a specific group of people. That will make promoting it easier.
In a competitive field like legal? Try something funny like compiling crazy outdated laws from each state. Publishing newspaper clippings of those actually charged would be even better!
Remember before publishing anything online make sure to carefully review copyright law for the country of origin, and your country.
Here you are taking information from several sources and creating something new. This could be as simple as using mapping software with a new twist. Check out Google Map Mania for examples.
Don't have a developer? There are other ways to aggregate information. It could be as simple as an infographic. Let's say You are in a health field in the US. You could create an infographic comparing life expectancy to pet ownership. Then target pet groups.
What's the advantage of an infographic? They can be given away for other sites to republish. Thereby creating more back links, and exposure.
With creatively and thinking outside the box you can create linkable material from public information. The trick is designing something that will target a specific group and promoting it to them. Then watch the back links develop.