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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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30 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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3answers
501 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
21 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
73 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
640 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
49 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
50 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
21 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
68 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
139 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, ...
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1answer
157 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
56 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
50 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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0answers
71 views

Indices of irregular polygon shape that account for different polyogn sizes

I have a set of irregular polygons, each representing the amount of space that underwent either erosion or accretion in coastal dunes over the last years. The polygons have different shapes, but ...
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2answers
164 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
312 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
21 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
44 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
70 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
262 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
66 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
54 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
160 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
366 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
165 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
1k 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
505 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
29 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 ...
2
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1answer
59 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
3k 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
96 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
229 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
52 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
88 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
73 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
39 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
131 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
62 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 ...
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3answers
1k views

What units are used for coordinates in geographic and projected coordinate systems?

I'm trying to grasp the basics of GIS but my literature seems to leave out some of the basic concepts (or it's just very vague). What units are usually used for coordinates in a geographic coordinate ...
4
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1answer
92 views

Standard direction format in GIS software

I am working on an application, where the user can place some items on a map. Some of these items have a direction, currently saved as radians where 0 is towards right/east. We want to enable the user ...
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1answer
270 views

In what units do area calculation in geographic coordinate system return?

Is it correct to call it degrees square? Will it be the same if calculate the area using Plate Carrée projection?
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0answers
132 views

Matching segments of different lengths

I'm trying to match small segments with a larger segment they are the most probably related to: relatively close, similar bearing, and facing each other. Here is a typical example of the data I have: ...
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0answers
111 views

Detrending DEM in floodplain?

I am after the same solution to Removing elevation trend over sloped surfaces? I am following the steps outlined, but in the last step it states: In this expression [X'] refers to the the x-...
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0answers
64 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 ...
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1answer
61 views

Where do 'line and point' holes come from?

It's quite common to find these topology errors when dissolving data: Census tracts dissolved by neighborhood using ST_Union (PostGIS) It's quite simple to understand the concept of a polygon donut ...
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0answers
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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 ...
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1answer
93 views

How does Ellipsoidal Height and Geoidal Height impact water flow? [closed]

I see this as a common theme Ellipsoidal height doesn't dictate water flow. Take a shot at explaining this. I think I understand this but it sounds like it would be of use to have a question about ...