I have been thinking to create a social network application built by using google earth api and sell/rent spaces for companies for their promotion on google earth via my web application. There will be a lot of coding and too much time will be spent on the project. So I am still not sure if it worths to make it. I am living in a town having a population of 60 000 and I want my application to provide users to walk and tour around the city and interact with the buildings which has companies inside.
Do you think it works ? How can I decide if it will work or not ? Is it doable ?
I think you need to do an opportunity evaluation to see if you have a commercial idea - or to discover how you can make it one. I have previously written an answer about this in detail here.
Basically, you look at all the business aspects of the idea to see if it is worth the time and money you will be investing. You can also find ways to improve the idea and make it more profitable. This is a process that experienced and successful entrepreneurs often use before they start investing time and money into a new idea. When you have finished, the information you uncover and the strategic decisions you make will form the core of your business plan.
I have some material on my site that can help you with this if you are unsure how to go about it.
You can never really know if it will work until the moment you launch it. You just gotta take the risk and give it your best shot.
Obviously, beta testing and pilot projects help, but the risk will always be there.