89
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Measuring accuracy of latitude and longitude
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 ...
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69
votes
Measuring accuracy of latitude and longitude
I think this XKCD is a perfect answer to this question :)
https://xkcd.com/2170/
- 1,113
30
votes
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What is this GIS Principle Called?
General
Geographers among other scientists seek for geographical patterns hoping that this will help them to better understand the processes that have produced these patterns. As you shown, this ...
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25
votes
What are the Differences Between TMS, XYZ & WMTS?
WMS is a protocol defined by the OGC for requesting rendered map images for arbitrary areas. Clients can make requests to it in a tiled pattern if they wish.
WMS-C is an extension for WMS created by ...
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25
votes
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Understanding reprojection?
Reprojection in GIS consists in changing the coordinates values of a dataset from one coordinate system to another coordinate system.
Let's take a one dimensionnal case as an exampple. Imagine that ...
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21
votes
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Hillshading makes crater-like depressions look elevated?
It may surprise you to find that most people likely do perceive your hillshaded DEM as containing depressions, however, this is not an uncommon experience. Here is the reason why. Ever since the ...
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19
votes
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Why does the same UTM northing give different values when converted to latitude?
This is perfectly normal behaviour in a transverse Mercator projection. The fact that a specific northing does not match a specific latitude (except for the Equator itself) can be easily visualized.
...
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17
votes
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Is it appropriate to create vertical scale bars?
The only reasons I can see why it would not be appropriate to use a vertical scale bar would be:
The audience does not want it or does not understand it
The audience associates the vertical scale ...
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17
votes
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Understanding the concept of m value
Those explanations are just what ArcGIS chooses to use to store in M values in specific contexts. They are not a standard or consensus. The other answers on the questions you linked also highlight ...
- 11.1k
15
votes
Is it appropriate to create vertical scale bars?
One reason would be (I think it is mentioned in one of the comments) is that the vertical scale bar may not accurately represent the distance of the railway track. This would be due to the likelyhood ...
- 76.1k
15
votes
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Difference between bounding box, envelope, extent, bounds?
I think you'll find there is a bit of overlap with these definitions. They're all very similar, in my opinion. However, ESRI has a glossary of GIS terms, so I just looked them up. The definitions are ...
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15
votes
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Why accurate area of all countries cannot be obtained using a single EPSG code, even if it corresponds to an equal-area projection?
What went wrong: EPSG:3395 is not equal area
The CRS you use, EPSG:3395, is definitely not an equal area projection. It is a World Mercator projection that heavily distorts areas, see here, including ...
- 73.8k
13
votes
Detecting branched polygon shape?
You could have a look at the following method : skeletonize your polygons and rather work on line type features related to your original polygon with a unique source polygon ID. I guess there's some ...
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13
votes
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Understanding resolution in vector maps?
The term resolution refers to the smallest details that can be distinguished. It is mainly used for raster data (resolution in time, in space or in spectral domain).
For a vector map, two other ...
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12
votes
What are the Differences Between TMS, XYZ & WMTS?
WMTS: http://www.opengeospatial.org/standards/wmts
TMS: http://wiki.osgeo.org/wiki/Tile_Map_Service_Specification
XYZ: https://en.wikipedia.org/wiki/Tiled_web_map
The three links above explain each ...
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12
votes
Measuring accuracy of latitude and longitude
The other excellent answers here are primarily about latitude. A degree of longitude shrinks from about 111 km at the equator to 0 at the poles, so the nominal precision of a decimal degree of ...
- 538
12
votes
What units are used for coordinates in geographic and projected coordinate systems?
A geographic projection will always be in degrees (or possibly radians) (the distinction between decimal and dms is one of formatting).
A projected crs can be in any units the designer wants, often ...
- 82.6k
12
votes
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Where do SRID numbers come from?
They're mostly from the EPSG - https://www.epsg-registry.org/
To be unique, you have to specify where they are from (basically a namespace - EPSG:4326, not just 4326). However most people will ...
- 12.9k
12
votes
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Higher resolution of country borders
Short answer
I think you should reevaluate your very concept of "official", high detailed source for all country borders worldwide. OpenStreetMap data comes close to a worldwide dataset with ...
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10
votes
How does a Spatial Reference System like WGS84 have an elipsoid and a geoid?
WGS84 is natively XYZ, like the International Terrestrial Reference Frames (ITRF), and you can use an ellipsoid model to convert to latitude, longitude, and ellipsoidal height. Ellipsoidal heights ...
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10
votes
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What units are used for coordinates in geographic and projected coordinate systems?
Geographic coordinates use angular units -- usually decimal degrees (DD), degrees and decimal minutes (DM), or degrees, minutes and seconds (DMS).
Projected coordinates use common linear units, ...
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10
votes
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What does M-value represent?
It is a measured distance along a route. A mile marker along a highway that is nominally 10.1 miles from some start (such as where the route crosses into a county) may not be exactly 10.1 miles. ...
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10
votes
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Average Cross Slope Calculation
Contours do not cross each other, so I cannot explain it using your example. Instead, let me illustrate what this ACS does by a picture below.
Looking at the pictures [1] and [2], you will find steep ...
- 31k
10
votes
Why accurate area of all countries cannot be obtained using a single EPSG code, even if it corresponds to an equal-area projection?
In addition to the fact that EPSG:3395 is not an equal area projection (therefore inaccurate for area measures), as mentioned by @Babel, a precise measure of the area requires a good projection. ...
- 49.8k
9
votes
What are Definition, Algorithms and Practical Solutions for Concave Hull?
QGIS does have Concave hull algorithm.
Parameters
Input point layer [vector: point]
put parameter description here
Threshold (0-1, where 1 is equivalent with Convex Hull) [number]
put parameter ...
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9
votes
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Should Legend entries be singular or plural?
I asked Dr. Aileen Buckley, Esri Cartographer for her advice. She wrote a blog post that explains when you should use singular and plural for legend items. I asked, ”Is there a cartographic convention ...
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8
votes
What is this GIS Principle Called?
In my opinion you have two different assumptions here. The modifiable Areal Unit Problem is one of them, like you wrote. This is the problem of artificial boundaries of administration areas.
But the ...
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8
votes
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MultiSurface Geometry type in QGIS: difference to MultiPolyon
The OGC standard about Simple Features describes LineString and LinearRing
A LineString is a Curve with linear interpolation between Points. Each
consecutive pair of Points defines a Line segment.
A ...
- 67.9k
7
votes
Is there a specific disadvantage to storing coordinates in geographic coordinate systems?
When I was involved in creating a European corporate-wide GIS it made sense for us to store geographical data in a common geographic reference system. In this case, the standard was European Datum ...
- 1,516
7
votes
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How can geographic coordinate system such as WGS84 draw on screen?
The latitude and longitude coordinates are just treated as planar coordinates.
Many GIS professionals refer to this colloquially as "unprojected". Some insist that any transformation from spherical ...
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