Feature Request: Add hotkey to navigate between data points / polygons

[nwisehart]

Steps to reproduce:

• go to /a11y-map/index.html
• navigate with keyboard to area with pop-ups
• enter a pop-up

Expected result:

• press [INSERT KEY HERE] to transfer to next data point (potentially ordered by legend?)
• current pop-up is closed and map moves to new point
• New pop-up is opened and read into live region
• Add feature to read current map position on close of pop-ups

Context:
In current format, a user with a visual impairment may be unable to navigate between data points in a orderly format, or unable to visit all data points without context of where they are.