# Questions tagged [gis-principle]

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

30 questions with no upvoted or accepted answers
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### Avoiding border effect in traffic modeling?

I'm creating a traffic model (using the Four-Step Travel Demand procedure). I have a road network (grey lines and grey node) and traffic injector/attractor (orange lines and orange nodes) as it can ...
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217 views

### Robust formula to get row,column of raster given X,Y

I'm looking for a robust method to get the row and column of a pixel in a raster, given the coordinates of the origin and the cell spacing. This seems like a problem with an incredibly obvious ...
• 13k
448 views

### Intersection and area calculations in geographic vs. projected coordinates

I think one should do intersection calculations when layers are in the same coordinate system, and one should do area calculations in the appropriate projected coordinate system. The order matters, ...
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262 views

### Correct planet radius, for calculating metres per pixel?

I am putting together some code to create tiles from various maps, for various planetary bodies, but I am not sure which value of planet radius I should be using, for indicating the metres/pixel ...
• 279
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### 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 ...
652 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 ...
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### 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 (...
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 ...
78 views

### Splitting linestrings based on their curvature

I'm looking for a method to split linestrings based on their curvature, more precisely if part of them could be considered a street corner. For example in the screenshot below, I'd need to split the ...
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### Assessing impact of spatial scale on derivative calculations and associated kernel size?

Full question: What is the most appropriate way to assess the impact of spatial scale on derivative calculations associated with typical 3x3 moving window kernel operations? This relates to a couple ...
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### Is aggregating points to areal units ever useful - Spatial statistics

I have a large point dataset of a population (By population, I mean that it was not a sample e.g. all houses in a county with an attribute such as size, price, age, etc.). Each point represents each ...
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52 views

### Do somebody know how factors as "age of data", "scale" and others influence the precision of GIS data?

Several factors may cause imprecision in datasets. As example of such sources, we should list: "age of data", "formatting", "scale", the technique employed to create the data and others. Each of them ...
434 views

### How does geofencing work?

How does geofencing work? I am aware that it creates a sort of polygonal bubble which can execute a certain action when you pass through it, but how does it actually do that without just constantly ...
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1 vote
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### 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 ...
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1 vote
118 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: ...
• 119
1 vote
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### 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 ...
• 19
1 vote
195 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 ...
1 vote
54 views

### Ground Control Points change when moving from one reference system to another?

In this question I'm interested just in the theoretical part. So, let's say we have such GCP in local reference system: (-2,14) (186,180) Label "Point 1", (-2,13) (211,6072) Label "Point 2", (-1,...
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1 vote
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### Deciding on classification method and number of classes for mean temperature

I'm trying to decide on the classification method: natural breaks, equal interval, quantiles, or manual and the number of classes for a map showing the mean temperature of places in Canada. The ...
• 167
1 vote
261 views

### Relative positional accuracy vs. registration error - what is the correct terminology?

I have several aerial orthorectified images that I am using for vector-based (points) change detection. I have calculated RMSE using sets of points on static landscape features in the images (e.g., an ...
1 vote
24 views

### Finding if journey passes near certain address/location?

I am thinking to create a website where people can share car journeys. Users can register a car journey and other users can find a journey. At the moment, when a user registers a journey, I save the ...
1 vote
286 views

### Is it valid to resample a raster from 1m to 3 feet?

I know that in general it is not a good idea to up-sample. I am curious if it would still be be a "bad idea" with a minor change like this from 1m resolution to 3 feet? Going to 3 feet would not ...
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1 vote
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### Ideal minimal area for watershed automatic delineation using DEM SRTM

I need to do a bunch of analysis on a city using for that, watersheds . As smaller the watersheds are, better are quality of my work. Due to the vertical accuracy of SRTM DEM, I know there are some ...
1 vote
40 views

### How to manage unique ID's for altered polygon

I'm working with administrative boundary polygons and am wondering when to keep the existing unique ID, and when to assign a new unique ID to a polygon. For example, if District A merges with District ...
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1 vote
921 views

### Calculating coordinates when only bearing of two points and distance between them is known?

I have bearing of two points 115 33' 09" and distance between these two points is 1464.36m. Is it possible to get the unknown coordinates from this data?
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### 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 ...
566 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 ...
343 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 (...
953 views

### Looking for a US state file for geofences with as few geofences per state as possible (so group islands with mainland)

UPDATED TO MUCH MORE DETAILED QUESTION I'm building a set of geofences to be installed on a GPS unit to track vehicles as they cross state lines. The list of geofences are simple latitude/longitude ...
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