How to convince and/or ask researchers to share data? I'm currently working on gathering data for my MSc thesis. The problem is, for my type of research, there is VERY limited data that is freely available. Specifically, I'm looking to acquire baseline population data for wild animal populations.

I've contacted a few organizations and NGOs asking if they have any data available and if they would be open to sharing it for a specific species.

One person seemed reluctant to share their data and wanted more information on my project - how can I convince them to share their data with me? There is hardly any other resources that have this type of information so it would really help me.  

Another sent me a number of papers they've written - but what I need from them is discrete locations (GPS coordinates) that they no doubt have as they have figures in their paper. However, for my research I need precise locations and estimating them from a figure is not ideal.

This is my first run at this, so I'm trying to figure out the best way to open up data sharing and collaboration. It's really important to me - but I also know that not all researchers think similarly. Especially when, at this point in my research I'm not 100% sure what I can offer them in return as it hinges on the data I can gather. Do I offer acknowledgement or authorship on my papers? Keep them updated with my progress and try to illustrate how I could help them?
First, I suggest you to be very clear with what you are working on (which is not evident to me yet), what is your  deliverable, your time schedule, and why the data they have are important for your project.

Then, there always is something you can offer in return, that may have value for them: from a bibliographic report to innovative mapping of the data. Many people work at nice data vizualization tools that rock. Just saying, because you were talking about GPS data. We have entered a world of data science, where you can do a lot with novel tools. 

Whatever the option, I would suggest to take some data you have, work on some awesome analysis method, and sent them as a pre-gift