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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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70 views

What comprises an organization's GIS budget? [closed]

Having read Good Subjective, Bad Subjective and other GIS Stack Exchange materials on what should and should not be asked on here, I'm confident there is a place for this question here, especially ...
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0answers
28 views

Great circle distance vs. ellipsoidal model

Suppose I have a javascript function: sortByDistance( a, // Single point b, // List of points method // ellipsoidal or greatCircle ) { // Returns b, sorted closest to furthest from a }...
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1answer
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The manual Dempster–Shafer theory in GIS? [closed]

I am looking for the manual Dempster–Shafer theory. Can you help me?
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2answers
71 views

Turning degrees into square kilometres (km2)?

After running raster layer unique value report I have got pixel number and area in degree. How can I turn it in square kilometres (km2)?
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1answer
126 views

Difference between Geodetic Distance and Great Circle Distance?

According to Wikipedia: The great-circle distance or orthodromic distance is the shortest distance between two points on the surface of a sphere, measured along the surface of the sphere (as ...
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2answers
45 views

Calculating haversine versus checking latitude and longitude digits after decimal point?

If I want to tell whether 2 points are close to each other, say at proximity of 50 meters, is it OK to compare both numbers up to a certain decimal point, for example the two points: 36.391155, -56....
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0answers
76 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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2answers
111 views

Understanding Inverse Distance Weighting Bulls Eye Effect?

Is the Bulls Eye Effect generally caused by a sample point with a high value being too far from other sample points? Or rather a sample point with a higher value than others close to it? What ...
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1answer
65 views

Understanding Vector Tiles?

I'm having trouble understanding the concept of a Vector tile. My understanding of Vector is point, line, polygon. So buildings, roads, areas etc. My understanding of Raster is a grid of pixels each ...
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2answers
113 views

Geometric difference between equal-area and conformal projection

For simplification, let's have a source light for a map projection. I know where to put the source light in order to get an orthographic, stereographic, gnomonic map projection, but I still don't ...
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0answers
39 views

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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2answers
582 views

Defining Latitude and Longitude before defining Datum?

Reference material: The Five Key Ingredients for Mapping the Earth There are five important steps to producing a map of the Earth's Surface. These are: sphere with north and south through the ...
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0answers
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What surface's area is used to compute area of country? [closed]

Premise: Earth's surface geometry is modelled by means of different geoids -depending on the objectives. The roughest and most basic are ellipsoids surfaces. Yet, on a small scale, e.g., area of ...
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1answer
30 views

Redefine (or reconfirm) Node and Vertex in 3D-GIS

Sorry if this sounds too broad and opinion-soliciting... I think the difference between Node and Vertex had been discussed before (for instance) Difference between node and vertex in GIS?, good and ...
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2answers
83 views

Detect the coordinate reference system based on an image

Given a map as image, how can I find out which coordinate reference system it has? The question is general, but here is a specific example. Below is the map for which I want to find the coordinate ...
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4answers
995 views

Understanding resolution in vector maps?

I'm developing a vector maps with detailed features such as road edges, cross walks, traffic lights , street lights etc., by using 3D points (x,y,z) without geo-referencing, generated from stereo ...
3
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1answer
51 views

Merging convoluted raster DEMs - what is this method and why use it?

This is more a theoretical question than practical, and I'm referring to 3x3 convolution kernels with online demo and the first comment after it. I have a raster elevation model and want to turn it ...
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1answer
75 views

How to only select lines (geometry features) going through a polygon? [closed]

I'm currently trying to select bridges (line features), from a shapefile containing roads, which go across water (a polygon). The problem is when i try to select features crossing or intersecting the ...
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0answers
32 views

Doing coregistration evaluation?

Let's say I have a reference image and a target image. And I'll use an application to do coregistration of this images. How do I measure how good the result is? I seek a general answer that is ...
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0answers
71 views

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 ...
3
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1answer
238 views

Hillshading makes crater-like depressions look elevated?

I have a 1 m resolution DEM of the seafloor of a field of depressions. Hillshading the DEM makes the depressions look like mounds instead. What I can do to fix this? My raster is projected in UTM, ...
2
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1answer
171 views

Agreed Upon Name for Rows in an Attribute Table

Is there an agreed upon name for the rows in an attribute table, perhaps one that would apply across different GIS software platforms? Esri uses "records" here, for example. They also have the ...
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1answer
77 views

plotting a circle in a spreadsheet

I can't get my head around plotting a circle on a big sphere (Planet Earth). I have a column that has 180 rows - 1 for each degree. The next row is each degree converted to radians. Easy so far. A1 ...
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0answers
56 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 ...
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2answers
314 views

Finding N,S,E,W lat/lon at a determined radial distance from an input lat/long [duplicate]

I am working on a project where I geocode a users address to get a lat/lon value. With that value, is there a way to find the latitude and longitude of points that are a set distance (eg. 100m) away ...
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2answers
564 views

Is the 180 west the same as 180 east?

I had a discussion about this topic with a co-worker. We are working implementing a GPS validation system, and I told him the longitude -180 (or 180W) is not a valid longitude because a valid ...
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0answers
22 views

Is there such a thing as no projection? [duplicate]

I was reading an article that said when we display a map in WGS84 many people call it no projection. But most definitely when you see the map it has been distorted on a 2D surface. Which got me to ...
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1answer
49 views

Non-geographic grids on maps

There are plenty of maps around, printed and otherwise, with numbered grids that do not directly equate to real-world coordinate systems. Typically these grids will have 0,0 in the bottom-left corner ...
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1answer
127 views

Calculating uncertainty for coordinates data?

I have a dataset of species distribution in latitudes and longitudes extracted from geo-tagged photographs. I have plotted them on a map to see how distribution looks like. My attempt was to check ...
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3answers
389 views

Using UTM vs Degrees for calculating distance? [closed]

I've been told that UTM is better for calculating distances on a map, however I can't see the reason for that, and I've got a lot of data that is not in UTM, so it would be good to know that I don't ...
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1answer
82 views

Determine Los Angeles neighborhoods based on coordinates

I'm new to the GIS world. I've read several sites and previous posts but couldn't find a satisfactory answer. I have a data set of ~400k coordinates from Los Angeles and would now like to determine ...
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1answer
63 views

Converting distance to coords?

I want to convert a coords interval (especially latitude) to real distance. I mean let's say we stay at the exact same longitude, but with 1 degree of difference in latitude. How many kilometers/...
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2answers
268 views

Spatial join and sum of attributes between 2 layers

I have on a spatial join issue : I need to perform a spatial join from a building shapefile to a grid feature class (200 * 200 meter). The spatial join needs to compute the sum of each attribute per ...
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1answer
479 views

Detecting branched polygon shape?

I have a vector layer with millions of polygons making continuous coverage. I need to classify them according to their shape. I am already using several shape indexes from landscape ecology like ...
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2answers
1k views

How to determine if a Polygon is inside another Polygon's hole

Given two valid polygons P and Q, what's the cheapest / fastest way to determine: If polygon Q is inside one of polygon P's holes (interior rings), or vice versa. (see illustration below) To the ...
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2answers
266 views

Moran test results - rejection of H0

I started with a linear model (lm) and I want to make some spatials models so I tried first a Moran test to lm. Can we reject the null hypothesis with a p value of 0.11 in order to continue working ...
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2answers
1k views

What is this GIS Principle Called?

I've forgotten the name of a particular GIS principle and need a refresher... Scenario: Let's assume there is some polygon which represents some administrative area. Let's say it's a square, for the ...
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1answer
2k views

Understanding reprojection?

One thing that I can't quite get my head around is Reprojection. It comes up a lot in questions on Stack Exchange, and there are plenty of How to questions and answers about specific issues using ...
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1answer
631 views

Where do SRID numbers come from?

We know what SRID 4326 means and what 3857 means but I do not know what these numbers mean. What is the minimum and maximum number for these SRIDs? I know it is a standard but how did they select ...
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1answer
32 views

Modifying projection in Arc-changing standard parallel in N. Pole Lambert Azimuthal

I'm working in a few targeted areas, and I wanted to project them all similarly. ROIs are on the order of 200 km x 200 km. For various reasons I'd like to use an equal area projection. I like the ...
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1answer
67 views

Interpolation of river pollution data

I have 6 samples of water quality parameters taken on a 10 km stretch downstream (Cooum River in Chennai), so it's basically the estuary. The river discharge and flow is extremely low, therefore I ...
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1answer
5k views

Difference between bounding box, envelope, extent, bounds?

Every time when I create a script to manipulate vector (point, line and polygon) in python I meet this doubt. What is the difference between bounding box (bbox), envelope, extent, bounds?
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1answer
101 views

Calculating change between two sets of district lines?

I'm using the Census Shape files for state legislative district lines for 2008 and 2012. I want to create a measure that indicates how much these lines have changed between these two time periods (...
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0answers
323 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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1answer
62 views

Pseudo-nodes Vs line simplification

I am confused, whether removing pseudo-nodes and line-simplification methods should be considered as the same concept. Line simplification is one normally done using Douglas-Peucker algorithm such ...
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1answer
112 views

Does line feature have one or two dimensions?

In the coursera class fundamentals of gis it's said that lines are one-dimensional feature and polygons are two-dimensional. Is this correct? if the line has a curvature two dimensions are needed to ...
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1answer
98 views

Calculating imprecision introduced by using WGS 84 coordinates as x,y in raster?

I have several coordinates provided in WGS 84 which I need to rasterize. For that purpose I simply interpret the lat,lon coordinates as x,y coordinates and I apply some scaling. So e.g. anything in ...
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0answers
41 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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3answers
143 views

Representing heights in GIS? [closed]

I've discovered, that I have no idea, how height is usually represented in GIS. For example, let's say we have software, that lets you create a mission plan for an UAV such as take off go to point ...
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0answers
70 views

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 ...