How do you calculate Shares for Instagram?

Shares for Instagram are calculated as the number of times the link to your Instagram post was shared on other social sharing sites: Pinterest, StumbleUpon, Reddit, Digg, Twitter, Facebook, Linkedin.

For some social networks (Blog, YouTube, Linkedin, Tumblr, Instagram, Slideshare, Vine, Vimeo) we additionally collect data from other places besides the channel (e.g., Disqus, Delicious, StumbleUpon, Reddit, Digg).

Read more about data collection sources here.

Where do you get geographical location info for Engaged Users in the Audience report?

From social network's public APIs.