Metropolitan’s conveyance and distribution system includes over 6,000 structures and substructures of various types, such as blowoffs, meter structures, valve structures, and pumping plants. Locations of these structures relative to the pipelines and feeders they are connected to are maintained within the ESG Geodetics and Mapping Team's IMDC system. This layer is a copy of the IMDC structures table, last published to EGIS on 25 February 2020.

As of October 2020, structures within this layer are classified as one of 39 structure types (STRUCTYPE) comprising 16 structure type groups (STRUCGROUP). Some examples of structure types within the AR structure type group include standpipes, surge chambers, and air release appurtenances. Where applicable, Maximo location codes are included for some specific structures, which can be used to identify Maximo assets (equipment) and work orders within the Computerized Maintenance Management System (CMMS). In some cases, this dataset also includes a couple of links to record drawings within EDMS for a given structure. As most structures will have a large number of drawings, this link is intended for convenience to assist staff with starting their research into record drawings.

Much of Metropolitan's infrastructure, appurtenances, and equipment are enclosed within structures. Thus, this layer is also an indicator of the various facilities and sites within Metropolitan's conveyance and distribution systems and can be used to indicate approximate locations of that enclosed equipment. This layer is not intended to include structures at treatment plants (though a few structures may be included, particularly those connected to feeders or pipelines).