# Tag Info

88

Here's my rule of thumb table... Latitude coordinate precision by the actual cartographic scale they purport: Decimal Places Aprox. Distance Say What? 1 10 kilometers 6.2 miles 2 1 kilometer 0.62 miles 3 100 meters About 328 feet 4 10 meters About 33 feet 5 ...

72

For ESRI its almost always going to be: Lat = Y Long = X It's easy to get backwards. I've been doing this for years but still need to think about it sometimes. On a standard north facing map, latitude is represented by horizontal lines, which go up and down (North and South) the Y axis. Its easy to think that since they are horizontal lines, they would ...

71

It doesn't matter at what longitude you are. What matters is what latitude you are. Length of 1 degree of Longitude = cosine (latitude in decimal degrees) * length of degree (miles) at equator. Convert your latitude into decimal degrees ~ 37.26383 Convert your decimal degrees into radians ~ 0.65038 Take the cosine of the value in radians ~ 0.79585 1 ...

57

POINT #1. lets differentiate Precision from Accuracy As it is clear from the picture we can talk about Accuracy of a measurement (e.g. 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 ...

40

The terms are medieval: latitude (n.) late 14c., "breadth," from Old French latitude (13c.) and directly from Latin latitudo "breadth, width, extent, size," from latus "wide," ... . Geographical sense also is from late 14c., literally "breadth" of a map of the known world... In the fourteenth century, most known-world maps made in the Christian and ...

30

I'll try to explain it in different terms: Earth's equatorial circumference is about 40,000 kilometers (25,000 miles). A latitude/longitude value breaks that distance up into 360 degrees, starting at -180 and ending at 180. This means that one degree is 40,000 km (or 25,000 miles) divided by 360: 40,000 / 360 = 111 25,000 / 360 = 69 (So, one degree is ...

25

This question assumes an ellipsoidal model of the earth. Its reference surface is obtained by rotating an ellipse around its minor axis (plotted vertically by convention). Such an ellipse is just a circle that has been stretched horizontally by a factor of a and vertically by a factor of b. Using the standard parameterization of the unit circle, t --> ...

25

The coordinates are in MGRS (Military Grid Reference System) which is a projected coordinate system. Those coordinates give you an accuracy of 0.1 meters since there are 10 trailing digits. You can batch convert the coordinates in online websites like this The first 3 charcters are the "grid zone desiganation" : 38R the next two characters are the 100,...

23

The principal radius of the WGS84 spheroid is a = 6378137 meters and its inverse flattening is f = 298.257223563, whence the squared eccentricity is e2 = (2 - 1/f)/f = 0.0066943799901413165. The meridional radius of curvature at latitude phi is M = a(1 - e2) / (1 - e2 sin(phi)^2)^(3/2) and the radius of curvature along the parallel is N = a / (1 - e2 ...

23

They are likely "Degrees, Decimal Minutes". Conversion to Decimal Degrees You can convert it to "Decimal Degrees" by diving the "Decimal Minutes" by 60 and adding the result to the Degrees: 21.440 / 60 = .3573333333 + 39 = N 39.3573333333 48.076 / 60 = .8012666666 + 120 = W 120.8012666666 Conversion to Degrees Minutes Seconds Or you can convert to "...

21

I think this XKCD is a perfect answer to this question :) https://xkcd.com/2170/

17

I always remember Longtitude as being "Long", where the lines do not change in length, and circle the globe. Also, Latitude being lateral, i.e. sideways

16

You need to have a projection() function to project the lat and long of your points onto the map. By default, a d3 geo path uses the albersUsa projection, so you could declare it explicitly: var projection = d3.geo.albersUsa(); You'll see this done in examples that don't use AlbersUsa, and by defining the projection you can modify it. Having it defined ...

15

The point at (0°, 0°) is not generally given a name All geographers, cartographers and surveyors ought to know the following, but I reference some sources anyway: According to Matt Rosenberg The point at which the equator (0° latitude) and the prime meridian (0° longitude) intersect has no real significance but it is in the Gulf of Guinea in the ...

15

You need to repeatedly add (or subtract) 360 to your value until it lies in the range of -180 - 180. So usually a pair of loops like: lon = -187; while(lon < -180){ lon +=360; } while (lon > 180){ lon -= 360; }

15

An answer that avoids conditionals and function calls: longitude = (longitude % 360 + 540) % 360 - 180 I wrote a quick microbenchmark at https://jsperf.com/longitude-normalisation and the conditional code seems to be faster (in Chrome on my machine) for 'reasonable' ranges of input values. In general you probably shouldn't be worrying in advance about ...

13

There are plenty of ways to do this using both open source (pyproj, gdal, postgis) and commercial libraries (ArcGIS). If it's just a one time work, you could use this service from Boundless: http://prj2epsg.org/search The service is: Prj2EPSG is a simple service for converting well-known text projection information from .prj files into standard EPSG ...

12

It depends on what you mean by 'Universal Coordinate System'. If you wonder whether most Professionals understand Latitude and longitude, well in that case it is pretty much universally understood. But if you ask, whether it is used by everyone, then the answer is a resounding, No. There are many reasons why people use projected coordinate systems instead ...

12

When you transform you always transform pair of points: ol.proj.transform([23.4, 42.5], 'EPSG:4326','EPSG:3857'); (this transforms from EPSG 4326 to EPSG 3857; the coordinates are [lon, lat])

11

Although geodesics do look a little like sine waves in some projections, the formula is incorrect. Here is one geodesic in an Equirectangular projection. Clearly it is not a sine wave: (The background image is taken from http://upload.wikimedia.org/wikipedia/commons/thumb/e/ea/Equirectangular-projection.jpg/800px-Equirectangular-projection.jpg.) Because ...

11

Looks like ogr2ogr has support for exactly this problem. The below is copied directly from that page: How do I flip coordinates when they are not in the expected order The EPSG has a recommanded order for geographic SRS where the coordinates tuples of a geometry must appear in the (latitude, longitude) order, whereas most GIS will properly display such ...

11

I've answered this question in passing while answering another of your question. The Greenwich Observatory was defined as a prime meridian, based on the observations by the astronomer Sir George Airy in 1851. London was selected as the official prime meridian for international maps by the International Meridian Conference in 1884. When you use a GPS, by ...

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Disclaimer: Any method you use to do this, especially with a consumer GPS unit, is going to be an approximation at best. If you truly want to know where the boundaries are, you will need to locate property pins/corners which might require a metal detector. Your best, safest option is to hire a professional land surveyor. No, those are not lat/longs in the ...

11

I propose a solution using PyQGIS: the several codes instantly work from the Python Console, but they can easily be implemented in separate scripts (see the edit at the end of the answer). Each script will return a new memory vector layer storing the inverted lon/lat coordinates for the geometries. I tested the solution on several datasets available from ...

10

As stated in the tool documentation for Calculate Field: Python expressions can use the geometry area and length properties with an areal or linear unit to convert the value to a different unit of measure (for example, !shape.length@kilometers!) These expressions are not usable with points or individual coordinates. Fortunately, you can use other ...

9

Your coordinates are likely in UTM (Universal Transverse Mercator) Eastings and Northings. You can convert UTM coordinates to lat/long online using many different sites. Here in one. You can also perform this calculation in excel or inside of a database if you can work out the formula. Alternatively you can perform the conversion inside of a GIS such as ...

9

Seems to be http://en.wikipedia.org/wiki/UN/LOCODE Coordinate syntax explained in http://www.unece.org/fileadmin/DAM/cefact/locode/Service/LocodeColumn.htm#Coordinates 1.10 Column "Coordinates" This column contains the geographical coordinates (latitude/longitude) of the location, if there is any. In order to avoid unnecessary use of non-...

9

A lat lays flat. Can't think of a matching one for longitude.

9

The trick of remembering latitude as 'ladder'tude always helped me. Think of a ladder standing up and the rungs of the ladder representing the E-W latitude lines.

9

From 3rd grade: lOngitude goes nOrth-sOuth

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