We Couldn't Map Water. We Could Map City Gas — a New Layer Born from One Comment

Hello from the MAPRISE team. This post isn't really a feature announcement — it's a record of what we learned after following up on a single comment, and the judgment calls we made along the way while turning that into a map layer.

A little while ago, we had the chance to show MAPRISE to a working real-estate professional. During that conversation, they asked: "The legally required disclosure statement (juuyou jikou setsumei-sho) has sections for water and gas — could those be shown on the map or included in your reports too?" Honestly, water and gas hadn't been on our radar until then. It was a good enough question that we decided to actually look into it.

The short answer: we couldn't map water. We could map city gas, for the Kyushu 7 prefectures. Here's the story, and the decisions we weren't willing to compromise on when turning it into a layer.

Water: why we set it aside

Water pipe network data is a required entry in the waterworks facility ledger under Japan's Water Supply Act, and every water utility holds it. More utilities are publishing this data online these days, but the primary purpose of that publication is to reduce individual inquiries from residents — it isn't intended for redistribution by a third party. Some utilities even require registration or an agreement before you can view it.

Checking the water utilities across the Kyushu 7 prefectures, only a limited number explicitly permit commercial secondary use. So we decided not to bring this into MAPRISE, and concluded that water supply should continue to be confirmed directly with each local utility desk. We don't see this as a criticism of any utility's disclosure policy — publishing data as a resident service and redistributing it commercially through a third party are simply different purposes to begin with, and we understand each utility's approach on its own terms.

City gas: why it was possible

General gas pipeline operators, on the other hand, are listed publicly by Japan's Agency for Natural Resources and Energy. Each operator also publishes its own service area through its wheeling (third-party access) supply terms, required under the Gas Business Act. Both are already-published documents, which meant we could extract factual information from them and turn it into a map.

Based on 87 supply-area records from 26 operators across the Kyushu 7 prefectures (Fukuoka, Saga, Nagasaki, Kumamoto, Oita, Miyazaki, and Kagoshima), we show the 249 target municipalities (government-designated cities counted by ward) in three categories on the map:

(As of August 2026. 14 records retain notes on partial supply areas.)

In the layer menu, we placed this under the "Lifestyle facilities / school districts" group — the same grouping as elementary and junior high school districts, since it's the same kind of local-infrastructure information.

The design decisions (the real point of this post)

We spent less time on the mapping itself than on deciding how finely to draw it. Two decisions, in particular, we weren't willing to compromise on, out of respect for the professionals who'd actually use this.

1. We deliberately did not use neighborhood-level (chome) polygons

Partial service areas described in wheeling supply terms are often written as road-based boundaries — phrases like "west of Municipal Road X" — that don't line up with the administrative boundaries of neighborhood (chome/oaza) polygons. If we colored by neighborhood polygon, a neighborhood that's only partially served would end up displayed as if it were served in full — a real misrepresentation.

We decided that if we couldn't draw at a resolution that was actually accurate, it was better to accept coarser detail than to risk misleading anyone — so we kept this at the municipality level. The on-map popup also states explicitly: "This only indicates that a service area exists somewhere within this municipality; it does not indicate supply across the entire municipality or confirm whether a specific parcel can be supplied."

2. We separated "no service" from "unconfirmed"

The other thing we struggled with was how to handle municipalities where we couldn't precisely read the service area from the published materials. In three cases, a general gas pipeline operator does exist, but the wording of its supply terms wasn't enough for us to confirm the exact area it covers.

It would have been easy to just color these as "no service" — but that would be factually wrong. Since an operator exists, there's a real possibility the area is actually served. "No operator exists" and "an operator exists but we couldn't confirm the area" are two completely different pieces of information, and conflating them would create misinformation. So we display these three municipalities as "unconfirmed," in a distinct color.

How this relates to the disclosure statement — stated precisely

Article 35, Paragraph 1, Item 4 of Japan's Building Lots and Buildings Transaction Business Act covers matters relating to the supply of drinking water, electricity, gas, and drainage facilities. What we've mapped here is reference information for the city-gas portion of that item only. Water supply, electricity, and drainage facilities still require separate confirmation as before, and this feature alone does not satisfy that item.

This data is also municipality-level information. It cannot tell you whether piping actually reaches a specific parcel. When preparing a disclosure statement, please use this layer as a first-pass reference point, and always confirm supply availability for the target parcel directly with the relevant general gas pipeline operator. MAPRISE is not affiliated or partnered with any of the gas operators listed.

What you see when you click

Clicking a marker or area on the map shows that municipality's status, the relevant operator's name, and its contact point.

Closing

This all started with an offhand comment from a professional who could actually picture using MAPRISE in the field. Seeing the concrete line drawn between "water is hard, city gas is possible" — from a "section of the disclosure form" angle we wouldn't have thought of on our own — was, honestly, a good experience.

That said, finding out what was possible doesn't mean we're going to oversell its precision. Keeping this at the municipality level rather than neighborhood polygons, and separating "no service" from "unconfirmed" — both were judgment calls made specifically to avoid misleading the professionals who'll actually use this in the field. We hope it helps with desk research, within the bounds of what it actually is: reference information.

Questions or feedback are always welcome at info@maprise.jp.

The city gas service area data introduced in this post is reference information created by MAPRISE based on the "List of General Gas Pipeline Operators" (Agency for Natural Resources and Energy, as of June 1, 2025) and the wheeling supply terms published by each general gas pipeline operator. Record counts and categories reflect August 2026, and MAPRISE is not affiliated or partnered with any individual general gas pipeline operator. This content is reference information only; always confirm supply availability for a specific parcel directly with the relevant general gas pipeline operator.