# How precise are these coordinates? **URL:** \ **Category:** Factual Questions\ **Created:** [March 30, 2024, 10:24pm UTC](https://boards.straightdope.com/t/how-precise-are-these-coordinates/999621 "2024-03-30T22:24:58Z")\ **Posts on this page:** 2\ **Page:** 2
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [July 17, 2025, 12:06pm UTC](https://boards.straightdope.com/t/how-precise-are-these-coordinates/999621/21 "2025-07-17T12:06:35Z")
Let’s be clear on the distinction between precision and accuracy. Including more digits (that is, more precise) doesn’t make a measurement closer to correct (that is, more accurate). There is often an implication of accuracy when the precision is high, but a sanity check can make clear when that is unlikely. ---
**Author:** ![Timz](https://avatars.discourse-cdn.com/v4/letter/t/6a8cbe/32.png) [@Timz](https://boards.straightdope.com/u/Timz)\ **Post date:** [July 17, 2025, 5:10pm UTC](https://boards.straightdope.com/t/how-precise-are-these-coordinates/999621/22 "2025-07-17T17:10:19Z")
No need to log in. Like he said, put the point of the arrow on the point you want and right-click to get the five-decimal lat-lon. Left-click on the displayed lat-lon and the 15-decimal lat-lon is copied to the clipboard. Six of those digits are definitely useful, and seven are halfway necessary, below. An elsewhere post of mine from a year or two ago: This post is about investigating Google Maps’ accuracy – specifically, how accurately you can measure distances off of it. If you’re not interested in that, no need to read any further. Google will give you a straight-line distance between any two points on the map, but it turns out you can get a much more accurate distance than the one Google gives you. (Some? Most? of the time, anyway.) A few feet east of the red marker [https://goo.gl/maps/dS1v59YwGTLDhX797](https://www.trainorders.com/discussion/warning.php?forum_id=1&url=https%3A%2F%2Fgoo.gl%2Fmaps%2FdS1v59YwGTLDhX797) you see the shadows of two posts – they’re four-inch steel pipes. Two more posts just east of the marker at [https://goo.gl/maps/HQgWaFZLFsJo6Q3bA](https://www.trainorders.com/discussion/warning.php?forum_id=1&url=https%3A%2F%2Fgoo.gl%2Fmaps%2FHQgWaFZLFsJo6Q3bA) Google says the southeast post of the west pair is 3275.4 feet from the southeast post of the east pair. Actual distance is 3281.1 feet, correct within 0.1 foot. A 0.2% error is typical for a Google distance; the problem is that when Google calculates the distance it assumes a spherical Earth, so in an extreme case (a north-south line at the equator, or at a pole) it’s off by 0.5%, that being how unspherical Earth is. Fortunately we can hope to eliminate that particular error, because Google gives us the latitude-longitude wherever we click on the map. We take the lat-lons at the ends of the line we’re measuring and calculate the distance ourselves, on the unspherical Earth. Good a guess as any: Google says the posts are at 37,80319465N 122.3174799W and 37.7997694N 122.3069758W. (You right-click on the map and it gives you the lat-lon to five decimal places; left-click on that lat-lon and it stores the lat-lon to 14 places I think it is.) On the GRS80/WGS84 spheroid those two lat-lons are 3281.35 ft apart; if we want to be quite correct we’ll cut it down to 3281.33 ft since we’re below the spheroid. So the error is 3 inches – for all we know, just because I can’t expect to get the cursor point in the exact right spot, even at maximum close-up. The lat-lons aren’t correct to 3 inches, of course. They’re probably off by 6 feet. But the error is the same 6 feet, in the same direction, for both posts. Two more pairs of posts [https://goo.gl/maps/cDM2zhggye2hPpSV7](https://www.trainorders.com/discussion/warning.php?forum_id=1&url=https%3A%2F%2Fgoo.gl%2Fmaps%2FcDM2zhggye2hPpSV7) [https://goo.gl/maps/XiHpkpoHiJ1xAd2D9](https://www.trainorders.com/discussion/warning.php?forum_id=1&url=https%3A%2F%2Fgoo.gl%2Fmaps%2FXiHpkpoHiJ1xAd2D9) As before, we get the lat-lon of the SE post in each pair. Based on Google’s lat-lons, the calculated distance from the west post to the next one is 492.58 ft; actual distance is 492.74 ft, again correct to better than 0.1 ft. Calculated distance post #2 to post #3 is 918.39 ft; actual is 918.12, Calculated distance post #3 to the east post is 1870.39 ft; actual is 1870.24. Judging by the shadows, the posts likely were photographed together, on one picture – no seams between them, where Google stitched together two pics. We have no idea how much area each pic covers, or how much error is introduced by a seam. But as it happens, we can easily enlarge the investigation. See the white dot at the center of the concrete rectangle, just southwest of the red marker? [https://goo.gl/maps/935UeVSad5b9b7WE8](https://www.trainorders.com/discussion/warning.php?forum_id=1&url=https%3A%2F%2Fgoo.gl%2Fmaps%2F935UeVSad5b9b7WE8) That’s the concrete around a fairly new survey marker; NGS gives the marker’s NAD83(2011) lat-lon correct to something like a centimeter. So we can see how far off Google is, and how consistent its error is. Turns out it’s more consistent than you’d have thought possible. Google’s lat-lon for the above mark is 6.1 feet from the actual position, in azimuth 290 degrees. Next survey marker is the concrete dot a few feet south of the red marker [https://goo.gl/maps/8NvZi2pQiG9oywQA7](https://www.trainorders.com/discussion/warning.php?forum_id=1&url=https%3A%2F%2Fgoo.gl%2Fmaps%2F8NvZi2pQiG9oywQA7) There, Google’s lat-lon is 6.28 feet from the actual lat-lon, in azi 288 degrees. Next marker is the dot a few feet SE of the red marker [https://goo.gl/maps/isEiQmDkGb3BDgdG6](https://www.trainorders.com/discussion/warning.php?forum_id=1&url=https%3A%2F%2Fgoo.gl%2Fmaps%2FisEiQmDkGb3BDgdG6) Error there is 6.46 ft in azi 292 degrees. Next marker is at the center of the fence rectangle just south of the red marker [https://goo.gl/maps/2zGQyYtMZMuorQvv8](https://www.trainorders.com/discussion/warning.php?forum_id=1&url=https%3A%2F%2Fgoo.gl%2Fmaps%2F2zGQyYtMZMuorQvv8) Error is 5.68 feet, azi 289 degrees. Next marker is next to the red [https://goo.gl/maps/TG6wUVxfnmfbu7dF8](https://www.trainorders.com/discussion/warning.php?forum_id=1&url=https%3A%2F%2Fgoo.gl%2Fmaps%2FTG6wUVxfnmfbu7dF8) Error 6.20 feet, azi 291 degrees. Last of the new markers is 3-4 ft NE of the red [https://goo.gl/maps/2qp9okLpMM6K1ieL7](https://www.trainorders.com/discussion/warning.php?forum_id=1&url=https%3A%2F%2Fgoo.gl%2Fmaps%2F2qp9okLpMM6K1ieL7) Error 6.20 feet, azi 293 degrees. There’s another mark at the foot of Clay St, downtown. It’s not visible on Google, but with a little extra work we can learn Google thinks it’s 6.10 ft from its actual, in azi 292 degrees. And one more, also not visible, set in the concrete block at [https://goo.gl/maps/um23MWQC9VVkZiTA8](https://www.trainorders.com/discussion/warning.php?forum_id=1&url=https%3A%2F%2Fgoo.gl%2Fmaps%2Fum23MWQC9VVkZiTA8) Google thinks the north corner of the block is 6.98 ft in azimuth 292.5 degrees from its actual position. Ignorant guess: maybe the error is larger here because this is the only marker that’s not at ground level – it’s a couple feet up in the air, and if the camera’s not vertically above it, Google can’t quite fix the resulting error. Which would mean Google doesn’t do as well when marks are at different elevations, instead of all being near sea level as my marks are. Maybe eventually I’ll get around to enlarging the investigation further, checking survey marks farther away. NGS has numerous NAD83(2011) marks in San Francisco and elsewhere, miles away from the ones I checked. (I ought to do it before an earthquake throws everything off.) I left out some details in the discussion above; if you have questions, I may have answers. Or maybe not. [Previous page](https://boards.straightdope.com/t/how-precise-are-these-coordinates/999621.md?page=1)