The Layers tab in the left panel controls how the map draws each kind of object, the underlay, and the results layers. Nothing here changes the model; the settings are saved in your preferences and the next session opens the same way.
One row per kind — rain gages, subcatchments, junctions, outfalls, dividers, storage units, conduits, pumps, orifices, weirs, outlets, map labels and the vertex handles of a selected link or subcatchment (shown while 50 or fewer objects are selected) — with:
All on, All off and Defaults act on the whole list. A kind that is switched off is neither drawn nor picked by a click, so it cannot be selected by accident while it is hidden.
Both are drawing aids, placed by their own scaling and not stored in
the .inp; a storm-sewer project's DXF underlay arrives here
when the project is opened (§13.1).
The model's own georeferenced image — SWMM's [BACKDROP],
placed from a world file — is a separate thing, controlled from View →
Backdrop (§3.9).
Empty until a run has finished, then:
Which variable colours the map, the class breaks, playback and the query tool are in the Results view (chapter 10); the layers tab only switches the overlay. With the overlay on, the map you edit is the map that shows the results, so a node's colour and its Properties are one click apart.
The map is drawn in a fixed stack, bottom to top:
The model's objects always sit above everything imported for reference, so nothing loaded under the network can hide a node you need to click. Only the reference layers can be reordered among themselves.