The gravity main layer is a polyline feature class that contains information about the location and attributes of more than 5860 miles of sewer lines of the City of Houston’s sewer collection system. According to the City's Infrastructure Design Manual, a sewer line is a public sewer located within public Right-Of-Way or Permanent Access (PAE)/Public Utility Easement (PUE) that is maintained and operated by the City. The gravity main feature class includes LS Pump Line, Collector, Siphon, and Trunk.

The GIS Services Group of Houston Water, Houston Public Works currently stores and maintains the dataset within a Relational Database Management System (RDBMS).

The data are derived from Plan and Profile Engineering drawings obtained from Block Map, As Built, Field Book, Taps and Meters, Metro, Autocad Data from GHW Project, Wastewater Reconciliation Project, Other Source (Operator Input), FVFL, FVFD, Field Verified with Control Number, and Construction Layer.