2 electric substations as single multipolygon - decision-making, and execution

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1

There are 2 electric utility substations near 32.393506, -97.485427.

They’re drawn as a single multipolygon with name ‘Johnson Switching Station’.

But property tax records show the two substations to be on separate parcels with separate owners. I think it’s incorrect to have them both drawn as the same object. The north substation is in a ~150 acre parcel owned by Oncor Electric Delivery Co. The south substation is in an 8 acre parcel owned by Brazos Electric Power.

My inclination is to break up the multipolygon, and just have 2 separate polygons. List the operator of the north polygon as Oncor, and the south as Brazos Electric Power. EIA GIS data lists the north substation as “Johnson,” so I figure I’d name that one the “Johnson Switching Station, and leave the south substation unnamed.

My questions are:

  1. Is it appropriate to use property tax records as clues when deciding how to tag infrastructure?
  2. What would be the right way to break up the multipolygon into individual polygons? I poked around in both the open street map online editor and in JOSM and I couldn’t figure how how to do it. Left to my own devices, I’d likely just delete it and create 2 new ways covering the two substations.

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2

This sounds like a reasonable concern, and your thinking is generally aligned with OSM practice.

  1. Using property tax records
    Property tax / parcel data can be useful as a supporting clue, especially for ownership and operator, but they shouldn’t be treated as absolute ground truth on their own. In OSM we usually prefer:

on-the-ground evidence (imagery, signage),

authoritative public datasets (like EIA),

and local knowledge.

In this case, the combination of separate parcels, different owners/operators, and distinct fenced facilities strongly suggests these should be mapped as two separate substations, even if they are adjacent or historically related.

  1. One multipolygon vs two polygons
    A single multipolygon is generally appropriate only when:

it represents one logical feature, and

the parts belong together conceptually (same operator, same facility).

If the north and south substations have different operators and ownership, splitting them into two separate polygons is the cleaner and more accurate approach.

  1. How to split it in practice
    You don’t need to delete everything and start from scratch:

In JOSM, you can open the relation editor, remove the parts that belong to the second substation, and then reuse those ways to form a new polygon.

If that feels too error-prone, creating two new polygons and deleting the old multipolygon is acceptable, as long as the new objects are well-tagged and clearly mapped.

For naming, using “Johnson Switching Station” only for the north substation (per EIA data) and leaving the south one unnamed (or just tagged with operator) sounds sensible.

Overall, your proposed approach is defensible and improves data accuracy.

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3

In the online editor (iD) you can spit a way with ‘x’ on both sides of the polygon, then extend the lines to touch the other end using ‘a‘ forming a closed loop, and then you can remove the ways from the relation in the side bar and add the new appropriate tagging on your empty way