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Comment by jjoonathan | Hacker News Reader

It's wrong if you ignore context -- but then, everything is.

The context is that it's in a database serving up business locations. How is the geographic area owned (or occupied?) by a business reduced to a point? They don't say, so it's clearly unreasonable to expect accuracy and precision beyond, say, property boundaries, and perhaps not even that.

It would be madness to infer that the extra digits denote precision beyond the crude bounds set by context.

It would be further madness to reverse engineer a property boundary -- an entire path of points -- from a single point in a database.

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You can click at arbitrary positions on those maps and get 6+ sig-fig values for those positions. And since the map displays a satellite representation of the property, is it really that extraordinary that people might consider it to be sufficiently precise enough to put in a fence?

FWIW, the error margin for 6 significant digits is around 11 cm. Accurate enough to point at a computer mouse.

The 2D pixels in the projected satellite image will never map to a precise gps lat lng coordinate. These gps coordinates are also just a rough approximation of dead reconned coordinate systems that actually define the parcels.

You can easily try and overlay county parcel data into google earth and see how many features don’t align with the sat imagery.

No? Then why do they appear to? Sure, a professional should "know better", but will a lay person who has the official GPS coordinates of their property lines (obtained at the time of sale)?

That's why people get concerned about this; that's why posts like this are important.

If the page in question listed something that could be construed as a property boundary, sure.

It doesn't.

Every new home owner gets a "plat" that outlines the boundaries of their property, including GPS coordinates. Using a tool (like Google Maps) to overlay a coordinate with a ground feature isn't exactly absurd.

What does that have to do with the Melbourne Open Data Portal?

If you want to argue that Google Maps could do more to highlight the accuracy/precision limitations of its projected imagery, I'd completely agree -- but that's a different argument.

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