Borstal vs Dartmoor

Borstal

name
  • A suburb, formerly a village, in Rochester, Medway borough, Kent, England (OS grid ref TQ7366). 

Dartmoor

name
  • A moor and national park in Devon, southern England. 

How often have the words Borstal and Dartmoor occurred in a corpus of books? (source: Google Ngram Viewer )