#78 Section 6 & #94 Section 3

Edits to section 6. Flesh out GIS example and restructure paragraph to include 'contextual' data in master table, metadata, or additional linking tables. 

Edits to section 3. Modify sentence 2 for clarification on modifications to raw. Add sentence 6 for link back to raw vs modified

[NB: I had some troubles updating my fork. I believe everything is up-to-date, but I'd make an extra check before merging changes. Also, sorry for not making a branch to allow for two pull requests.]