locus vs tract

locus

noun
  • A place or locality, especially a centre of activity or the scene of a crime. 

  • A fixed position on a chromosome that may be occupied by one or more genes. 

  • The set of all points whose coordinates satisfy a given equation or condition. 

  • A passage in writing, especially in a collection of ancient sacred writings arranged according to a theme. 

tract

noun
  • An area or expanse. 

  • Part of the proper of the liturgical celebration of the Eucharist for many Christian denominations, used instead of the alleluia during Lenten or pre-Lenten seasons, in a Requiem Mass, and on a few other penitential occasions. 

  • A series of connected body organs, such as the digestive tract. 

  • A commentator's view or perspective on a subject. 

  • Continued or protracted duration, length, extent 

  • A brief treatise or discourse on a subject. 

  • A small booklet such as a pamphlet, often for promotional or informational uses. 

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