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Questions tagged [gis-principle]

Use for questions which involve a GIS principle or theory and are software agnostic

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3 answers
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Segmentation of a network at branches from one complex boundary polygon

If I have the polygon defining boundaries of a river network, is there any way to directly segment the tributaries out using geospatial data analysis? To elaborate, I am looking for a workflow more ...
MathX's user avatar
  • 163
1 vote
0 answers
22 views

How to use Lagrange interpolation method for station lies between a grid?

I have rainfall data for a catchment from 1990-2020 in grid format. But my station of interests lies in the grid, how to apply the interpolation to that station. I'm not sure if I'm proceeding ...
Hydra's user avatar
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0 answers
73 views

Regarding Geographically Weighted Regression (GWR) for non-linear problems

I am new to this topic. I am referring to this Geographically Weighted Regression tutorial. From my understanding, GWR does a weighted regression to model the dependencies between exploratory and ...
gis_grad_student's user avatar
0 votes
2 answers
87 views

What are the QGIS words for my 4 types of data?

My project has 4 types of data: a raster satellite view (Google Maps), to be the base layer and geolocated by three points (CSV) that apply to visible points on the raster map; individual points: ...
johnsankey's user avatar
-1 votes
2 answers
107 views

Using GIS to determine which properties have lake view

I'm a real estate agent in the Finger Lakes region of Central New York. Sometimes my clients want a house with a lake view. I am considering commissioning someone to build a map of all the nearby ...
Matt's user avatar
  • 15
0 votes
1 answer
168 views

Reason for existence of single parts vs. multipart layers

Vector layers can consist of single part or multipart layers. What is the reason for creating separate formats for that? It is perfectly possible to create a multipart layer and still create just one ...
Babel's user avatar
  • 72.9k
1 vote
0 answers
156 views

What does unit mean in spatial reference system?

Each spatial reference system contains a definition of a unit. The rectangular coordinate systems mainly use meters, the spherical ones use degrees. You can see the unit of a srs for example here: ...
mz71's user avatar
  • 119
3 votes
1 answer
115 views

Does intesect result change with CRS choice?

Question Before (some) spatial analysis, we need to make sure the coordinate reference systems of the layers are the same. I am doing intersect with two layers. I did that under a coordinate before. ...
Kang's user avatar
  • 49
5 votes
1 answer
250 views

Least cost path: what does least cost value represent, based on slope raster layer

Context and question I have a raster layer with slopes in percent and used the least cost path plugin in QGIS to calculate the least cost path from start to end. I try now to understand what the ...
Babel's user avatar
  • 72.9k
3 votes
1 answer
345 views

What value does slope represent, how is it calculated from neighboring cells of a raster DEM?

In QGIS, I have a Digital Terrain Model. Using Slope (Menu Raster > Analysis > Slope..., in fact using GDAL Slope algorithm), I get an output raster, either in percents or degrees, the same ...
Babel's user avatar
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-1 votes
1 answer
130 views

How do you interpret a DEM? [closed]

I have been asking myself a question for some time. How do GIS experts interpret a DEM (1) ? In my opinion, there are two ways of interpreting the value of a DEM pixel : Consider that the pixel value ...
Atm's user avatar
  • 1,537
1 vote
1 answer
47 views

Something like map algebra or cell statistics for vector format

I work in environmental consultancy and I have recently been tasked with generating the 'Environmental Zoning' for a road project. I use GIS in my everyday work but nothing too advanced. I'm not sure ...
Dan's user avatar
  • 31
1 vote
1 answer
359 views

Writing about GIS methods on the example of QGIS

I am preparing a thesis that relies heavily on GIS, specifically using the QGIS platform to calculate area extents and similar types of data. I have only recently learned how to use GIS technology so ...
Luke Miller's user avatar
1 vote
1 answer
368 views

How Neighbor Contiguity Algorithm actually works

I want to identify neighbors based on queen or rook contiguities in a programming language that does not have the feature yet. I know that tools like spdep, pysal, geoda, and ArcGIS all implement this,...
thus__'s user avatar
  • 179
0 votes
1 answer
234 views

Choosing projection system to use when georeferencing PDF maps

I need to georeference a PDF map and digitize the features on the map into a shapefile using WGS84. Is it best to georeference the PDF map and digitize the associated features in a local projection ...
Ian Moffit's user avatar
1 vote
1 answer
319 views

Latitude represented as a Matrix

I have some NetCDF data where I have a few variables lat : dimensions - (x,y) lon : dimensions - (x,y) x : dimensions - (x,) y : dimensions - (y,) temp : dimensions - (year, y, x) I am struggling a ...
user144483's user avatar
0 votes
1 answer
135 views

Voronoi and distance to the nearest point

I was convinced that Voronoi polygons were created so that each location in a polygon is closer to the origin point present in that polygon than to any other seeds In Snow's famous case study in Soho, ...
Wilcar's user avatar
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3 votes
1 answer
138 views

Identify the algorithm (not code) for QGIS native tools

The question For someone with no knowledge in C++ (programming language used to write QGIS code), is there a way to identify based on which algorithms the different QGIS native tools are written? ...
Babel's user avatar
  • 72.9k
3 votes
1 answer
233 views

Are contiguity matrix and adjacency matrix the same?

I'm am sorry for that beginner question. To start the calculation of a spatial auto-correlation value, the book I'm reading writes that we will starting to construct a contiguity matrix. Looking at ...
Marc Le Bihan's user avatar
5 votes
1 answer
153 views

How is datum used in assigning lat and long to point on Earth's surface?

It's accepted wisdom that geographic coordinate systems require a datum in order to assign lat/long to a point on Earth's surface. However, every point in 3d space already has 3d polar coordinates ...
Sideshow Bob's user avatar
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0 votes
0 answers
604 views

Spatial indexes with RTree for polygons

I am trying to understand about how R-tree works for polygon data. In other words, polygon is a list of vertices (points), however, I am wondering how spatial index can recognize the order of points ...
Masoumeh's user avatar
3 votes
0 answers
713 views

Is there a relationship between driving distance and straight line distance?

For fun, I created an FME workflow that emails me the 10 cheapest fuel princes within 10km of my house. I calculate both the driving distance along roads and the straight line distance. Knowing that ...
Fezter's user avatar
  • 21.9k
9 votes
1 answer
3k views

MultiSurface Geometry type in QGIS: difference to MultiPolyon

Adding a new temporary scratch layer in QGIS, selecting the Geometry type, there are different options, between else MultiSurface. In the documentation, I could not find any information about this ...
Babel's user avatar
  • 72.9k
2 votes
2 answers
1k views

How to interpret Tobler’s First Law of Geography?

Waldo Tobler's First Law of Geography is an axiom in GIS which states that "everything is related to everything else, but near things are more related than distant things" (Tobler, 1969). ...
HP-Nunes's user avatar
0 votes
1 answer
142 views

Confusion in longitude range, why do they start at 80? [closed]

In one of our notes in the university, there's a paragraph about latitude and longitude that tell us this: Geographic coordinates are the earth's latitude and longitude system, ranging from 90 ...
juztcode's user avatar
  • 103
3 votes
1 answer
225 views

Naming convention for ways of defining direction

The following two conventions for defining direction are very common, but what are they called? 0 at north, clockwise 0 at positive x-axis, counterclockwise Background: I'm writing a function that ...
blupp's user avatar
  • 141
7 votes
2 answers
2k views

Higher resolution of country borders

I have been looking and looking for a long while, but I was unable to find any freely available datasets for country borders with resolution higher than 1:1000000. I found this strange as I thought ...
David Kan's user avatar
14 votes
2 answers
1k views

Why accurate area of all countries cannot be obtained using a single EPSG code, even if it corresponds to an equal-area projection?

I would like to check if using different equal-area projections lead to near-identical area estimation for a list of countries. Importing modules: import numpy as np import geopandas as gpd import ...
zabop's user avatar
  • 2,214
2 votes
0 answers
48 views

Are there any mass-preserving raster projection algorithms?

Raster maps (e.g. as a GeoTIFF) can be reprojected using tools like gdalwarp. While these tools do a decent job to project images, they are not truly mass-preserving, i.e. the total sum of the values (...
p.w.bogaart's user avatar
1 vote
2 answers
1k views

Efficiently converting/storing WGS84 Lat/Long as Integers

I'm a GIS newbie and I'm trying to figure out how I might store WGS84 coordinates as an integer efficiently. I could simply multiply it (10e7 for example) but I feel like this must be a problem that's ...
JasonG's user avatar
  • 111
2 votes
1 answer
501 views

Accuracy of raster cell size area to real world area

I read from somewhere here that a UTM raster's pixel count ratio is 1 pixel = 1 meter. I am working on a raster that says the island is 4.03 km² in area but a quick google search says the island is 4....
Marc James's user avatar
2 votes
0 answers
124 views

Single numbers for accuracy and resolution for vector and raster data?

This question is meant as a modelling question, not having to do with particular data formats. It was edited to better separate spatial accuracy and resolution (precision). In order to make the ...
user1867448's user avatar
3 votes
1 answer
581 views

Why does cubemap projection preserve lines of longitude but not latitude?

My understanding of cubemaps is as follows: To create a cubemap from a sphere, we project from the centre of the sphere outwards, onto the faces of a cube. Each face of the cube therefore represents ...
Rob S's user avatar
  • 41
4 votes
0 answers
411 views

Is there a raster data format that can store dates instead of numeric values?

When storing spatiotemporal data, there is a need to store dates or time data. I know raster files can store numeric data (integer or float), but what about storing of dates data? I'm currently ...
Abel Melquiades Callejo's user avatar
0 votes
2 answers
750 views

What is the principle of pooling in ArcGIS Server?

If I understand correctly, pooling an AGS Service means that when a client connects to a service, an instance is created and an ArcSOC process is executed. Setting minimum to 0 thus doesn't start the ...
Robert Buckley's user avatar
1 vote
0 answers
97 views

Why are some maps shown with polar coordinates (azimuthal) and some Cartesian (cylindrical)

I am very new here, and in no way am I a cartography expert like all of you here. I am currently doing a math paper on map projections, and I have noticed that some projections (mainly azimuthal) are ...
Steven's user avatar
  • 19
1 vote
1 answer
233 views

Is topology stored explicitely in vector layers or is it derived from stored geometry information?

In vector layers, different types of information are stored like: Geoemtry Attribute data Meta data (like filename, projection etc.) Spatial indices However, what about topology? Is it an explicit ...
Babel's user avatar
  • 72.9k
0 votes
0 answers
360 views

What's the theory (principle) behind shapely.ops.polygonize?

I am learning Python package Shapely, but quite confused about the principle behind the polygonize function --- shapely.ops.polygonize. How does this function work to polygonize a set of lines (...
Yi Wang's user avatar
12 votes
2 answers
5k views

Understanding the concept of m value

As far as I understand, the m value "is a measured distance along a route" (similar answers here), thus similar to the mileage of a car driving over a highway. The m value defines the point ...
Babel's user avatar
  • 72.9k
2 votes
3 answers
105 views

Figure out location of city direction sign in image - friday fun project

So I came across this image and wondered where it could be located given the directions and distances. But I started to realise that the sign is all wrong. I'm guessing the Greek alphabet one is ...
user3390486's user avatar
10 votes
1 answer
2k views

Why does the same UTM northing give different values when converted to latitude?

I'm converting two coordinates from UTM to latitude/longitude. The coordinates are: Easting: 657787 Northing: 7795664 and Easting: 658144 Northing: 7795664 Both from zone 23S (EPSG:31998) or 23K (...
Rodrigo's user avatar
  • 772
1 vote
2 answers
80 views

Storing information for each segment of spatial line

I have some spatial lines from a shapefile representing roads. I'd like to attribute to each segment an information, for example the state of the segment or more generally a scalar that gives an ...
JRR's user avatar
  • 9,464
-2 votes
2 answers
716 views

Concept behind longitudes

Why longitudes are not parallel and why do they meet at the poles? What problem would have happened if like latitudes they were parallel circles running from west to east? I would request the ...
user166598's user avatar
2 votes
3 answers
1k views

Understanding map projection coordinate systems

I have been playing around with a variety of map projections for the purposes of transforming between various representations. The thing that I still don't quite understand is how to interpret the (x,...
marcman's user avatar
  • 121
1 vote
0 answers
196 views

Checking if network has connection errors

I have given a network of a city in dwg. I made a dxf that only contains the network itself, and created a layer for every type of pipe (like 25KPE, 80KPE etc...). How do I check if the network is ...
Mezobot93's user avatar
0 votes
2 answers
2k views

Determining if two locations are duplicate

I'm working on an app that will display drugstores in a map. I have a table that has all drugstores, each with its Lat/Lon. We used several different sources to add the data to the table: the ...
fdkgfosfskjdlsjdlkfsf's user avatar
1 vote
1 answer
418 views

Changes made to shapefile

If I take a Natural Earth shapefile and delete all countries except one - This will affect that original shapefile. Can I take that shapefile duplicate it and use that shapefile to delete all ...
213's user avatar
  • 65
3 votes
1 answer
97 views

Seeking documentation about non-iterative UTM to Lat-Long projection formulas

In Hager, John W., James F. Behensky, and Brad W. Drew. "The universal grids: Universal transverse mercator (utm) and universal polar stereographic (ups)." DMA technical manual 8358 (1989). I ...
Federico's user avatar
  • 237
1 vote
0 answers
33 views

Deciding when to use projected coordinate system (PCS) or geographic coordinate system (GCS)? [duplicate]

While I understand the technical differences between them both, I'd like an expert's breakdown of criteria to look out for that would determine when I should use a PCS or GCS. I understand that a PCS ...
tree123456789's user avatar
6 votes
1 answer
914 views

Average Cross Slope Calculation

My county ( Pima, Arizona ) uses a number called “average cross slope” which they define as ACS = (I * L)/A where I = contour interval L = length of contour lines in the area A = area ...
Charlie Burns's user avatar

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