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1500 questions
39
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1 answer

What is the default projection in Leaflet?

I've read an API documentation for Leaflet on its site, but I can't realize: what is a default projection to view maps? It was written about spherical and elliptical Mercator and Equirectangular - so which of this three? Or does it depend on tile…
Anton
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9 answers

Creating polyline-based "heatmap" from GPS tracks?

This winter I am planning to track my downhill skiing/snowboarding using a GPS. Most of my riding will occur at the same resort. I would like to be able to create a sort of "heatmap" that shows the amount of runs that I have made in a given area. …
RyanKDalton
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39
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9 answers

Machine Learning Algorithms for Land Cover Classification

I am interested in learning what software exists for land classification using machine learning algorithms (e.g. k-NN, Random Forest, decision trees, etc.) I am aware of the randomForest package in R and MILK and SPy in Python. What open-source or…
Aaron
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39
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6 answers

Creating square buffer around point feature using ArcMap

I would like to create a square buffer from a point feature but I do not understand the code that goes into it. Similar questions have been asked on the forums.esri website but that was over 10 years ago, and it did not work when I tried the…
Kimball
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39
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5 answers

Iterating over map layers using PyQGIS

I'm having trouble figuring out how to iterate over map layers. I can access the currently highlighted layer in the table of contents via iface.activeLayer() but I want my code to operate on all layers. I don't see anything in the API that provides…
spencerrecneps
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39
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5 answers

Generalizing polygon file while maintaining topology in QGIS?

I have a polygon Shapefile, which I need to generalize. How can I generalize the poligons and ensure that there are no topological errors like "slivers". I already tried: Vector -> Geometry Tools -> polygones to lines Vector -> Geometry Tools ->…
Kurt
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39
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3 answers

Assign multiple colors to features within a single vector layer

I want to give multiple colors to different features within a shapefile based on attribute values , is this possible in QGIS ? If yes what is the procedure ? Is there a way to provide color by means of hexadecimal codes ?
GeoH2O
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39
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7 answers

Performing Raster Reclassification in QGIS

Is there a way to perform a reclassify of a raster image in QGIS? In ArcGIS Desktop you can do that in Spatial analyst Tools→Reclass→Reclassify
Vassilis
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39
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6 answers

Increasing speed of crop, mask, & extract raster by many polygons in R?

I'm extracting the area and percent cover of different land use types from a raster based on several thousand polygon boundaries. I've found that the extract function works much faster if I iterate through each individual polygon and crop then mask…
Luke Macaulay
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38
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4 answers

Overlaying spatial polygon with grid and checking in which grid element specific coordinates are located using R

How can one use R to split a shapefile in 200 meter squares/sub-polygons, plot this grid (incl. ID numbers for each square) over the original map below, and evaluate in which square specific geographic coordinates are located. I am a beginner…
majom
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38
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4 answers

Separate polygons based on intersection using PostGIS

I have a PostGIS table of polygons where some intersect with one another. This is what I'm trying to do: For a given polygon selected by id, give me all of the polygons that intersect. Basically, select the_geom from the_table where…
atogle
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38
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9 answers

Calculating latitude and longitude of points using QGIS

How do I easily calculate the lat/long of points using the QGIS Field Calculator? I saw a previous related question (Using QGIS API and Python, to return latitude and longitude of point?), but it deals with a more advanced approach. In ArcGIS…
djq
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38
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10 answers

Adding Attribute data to shapefile?

I can display a shapefile in openlayers but I need to add some attribute data. I can open the dbf file in excel but there is no save as option in excel to the updated file as a dbf. What is the best way (or software to use) to add attribute data…
ChrisJ
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38
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4 answers

Simple thematic mapping of shapefile using Python?

I wish to visualize geographical data in Python, without using ArcGIS/ArcPy, and make a map. On the internet I found how to make a thematic map using Python: Here is some code that I tried: import shpUtils import matplotlib.pyplot as…
NYannickske
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38
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3 answers

What is approximate error of Pythagorean Theorem vs. Haversine Formula in measuring distances on sphere at various scales?

Many people when first trying to calculate distances between two longitude / latitude pairs ask if Pythagorean theorem works as an appropriate distance function. Most often people answer "no, the Pythagorean theorem only works on a 2D Euclidean…
Amos Budde
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