It's good to know that the meter was originally defined by the French, around the time of their revolution when they were throwing out the old systems and zealously replacing them by new ones so that ten million of them would take you from the equator to a pole. But that doesn't matter. Furthermore, a degree of longitude east-west is about the same or less in length than a degree of latitude, because the circles of latitude shrink down to the earth's axis as we move from the equator towards either pole.
If your accuracy need is sub-centimeter, then you need at least seven and probably eight decimal places, but more will do you little good. Using these ideas we can construct a table of what each digit in a decimal degree signifies:. As it is clear from the picture we can talk about Accuracy of a measurement e.
GPS measurement if we already know the actual value exact position. Then we can say how accurate a measurement is. On the other hand if you have some measurements and don't know the actual value you can just talk about the precision of the measurement.
If you are going to speak in cm or mm scale, it may be better to also consider the earth as an ellipsoid and not a sphere. Here is another table to show the changes:. As you can see it is not correct to say e. This means that one degree is 40, km or 25, miles divided by :. For fractions of a degree, you divide it by 10 for each decimal place, as ChethanS's chart nicely demonstrates in km :. The other excellent answers here are primarily about latitude. A degree of longitude shrinks from about km at the equator to 0 at the poles, so the nominal precision of a decimal degree of longitude increases as you get closer to the poles I am making no comment on the actual precision or accuracy of any given measurement.
Then the nominal precision of a longitude measurement at a given latitude is just determined by moving the decimal point; for example, at 40 degrees N, one degree of longitude is about 85 km and the precision of the first decimal at latitude 40 N therefore has a nominal precision of about 8.
You'll notice that 8. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Measuring accuracy of latitude and longitude? Ask Question. Asked 10 years, 7 months ago. Active 1 year, 7 months ago. Viewed k times. Improve this question. Saurabh Saurabh 5, 3 3 gold badges 15 15 silver badges 8 8 bronze badges. The answers here are good.
I thought I would add to the answer by relating how the digits in longitude are affected by latitude. Positive latitudes are north of the equator, negative latitudes are south of the equator. Positive longitudes are east of Prime Meridian , negative longitudes are west of the Prime Meridian.
Latitude and longitude are usually expressed in that sequence, latitude before longitude. The radius of the semi major axis of the Earth at the equator is 6,, The equator is divided into degrees of longitude, so each degree represents , The number of decimal places required for a particular accuracy at the equator is:.
A value in decimal degrees to an accuracy of 4 decimal places is accurate to It delivers both precise and accurate information. Sometimes its data gathered from centroids. Precision can be measured by the number of decimal places in the latitude and longitude provided. The number of decimal places correlates directly to the level of precision. But five decimal places can accurately hone in on an individual tree, and six can identify a person.
With so much precision riding on a single decimal place or two, you can see why it matters so much when it comes to targeting. Even a difference of 10 meters as between rows three and four represents the difference between useful and not useful for Blis.
At row four, a consumer may be in the hair salon they visit every week. At row three, they could be across the street buying coffee. Using Google Maps, you can see for yourself how precision works with respect to decimal places. Type in your address, then look at the URL. The coordinates are within the URL, right after the actual address I typed in: Anything beyond this is really impractical, even for our purposes. If you take those coordinates and put them into a tool like LatLong.
Now, take a digit off each number and search again. If you mean, strictly in the storage of a value in two DB columns, then perhaps. However, given values don't just sit in DB columns unused, the implicit assumption that there will be proximity queries written against these values. And holding this fairly pragmatic assumption then means all of the issues of it being an unreliable approximation continue to hold.
If one FLOAT value and the 'next' value are so close to each other in value that you can't tell one city or vehicle or person or flea from another, then the rounding and representation errors don't matter. You appear to be missing the point.
Any attempted query is going to be implicitly using equals, if not explicitly. And this assumes you aren't going through other layers and languages with the values, strictly staying inside of SQL Server.
Show 2 more comments. If you click locations on Google Maps, you get latitude and longitude with 7 decimal places. Savage Savage 2, 1 1 gold badge 27 27 silver badges 33 33 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown.
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