# Tagged Questions

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

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### Convention for azimuths

I need to compute the azimuth between 2 x,y locations, call them S and R. I know that it is simply done with atan2 (dx,dy) where dx and dy are the difference in the x,y coordinates for S and R. My ...
101 views

### Quantitative vs Qualitative heatmap

I'm having a debate with a colleague of mine over whether generated heat maps are quantitative or qualitative in nature. The underlying data source is GPS points. The GPS devices that we use are ...
27 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 ...
16 views

### Guideline on how to reference units and intervals in the legend

I often use some kind of elevation data in my maps in form of grids and contours. I never really put much attention to how to properly specify units and intervals in the legend but now polishing my ...
36 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 ...
71 views

### Reprojecting raster from one CRS to another?

I have a .tif raster file which is based on some projected coordinate system (for example: NAD 1983 State Plane California). I would like to export this raster as a .xyz file, but also reprojecting it ...
25 views

### 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 ...
48 views

### Removing every second row and column cells from a raster file

I have a SRTM 3 arc second topography model (.tif file). If I remove every second row and column of cells from the grid, can it be said that the model becomes a 6 arc second? Or does SRTM 3 arc ...
120 views

### What would a simple hillshade algorithm be?

I'm curious how GIS systems actually generate a hill-shade from input data like a raster DEM layer. I'd like to implement my own in software (mostly for fun/learning) but I want to start with a ...
47 views

### Formula for Nicolosi Globular Projection

What is the formula for the Nicolosi Globular projection? In other words, what is the function that maps the coordinate (φ, λ) on the sphere to the coordinate (x, y) on the plane? You can assume ...
46 views

### How is width commonly defined for areal features?

Map generalization guidelines, for instance applicable to CORINE Land Cover or Polish BDOO databases state inclusion criteria for areal features like "area should be > 250 000 m^2 and width should be >...
148 views

### How big does a circular geofence need to be for the curvature of the earth to matter? [duplicate]

I'm working on adding geofences to a mobile application. I know the proper way of calculating distance between two points on a sphere is using the great-circle or Haversine formula. I don't know if ...
33 views

### which projection are best for large continents [closed]

which projections are best for large continents and mid-latitudes
47 views

### Calculating scale for printing on paper

I will be making PDFs with maps on them. Two pages, one a4, one a3 format. Both will print the same thing, just one is going to be larger. Question - what scale do I print on the PDF? The number. If ...
24 views

### Does sinusoidal projection have constant scale factors in all directions?

I know that no map projections preserves all distances. However, looking at the definition of the sinusoidal projection: y = R * phi x = R * lambda * cos (phi) , where R is the radius of earth. ...
34 views

### How do we call the plane a latitude circle is in?

I was just wondering if there is a proper term to refer to the plane that contains a circle of latitude. I know for the special case of equator, that plane is called the equatorial plane. What about ...
84 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 ...
221 views

### Rounding Coordinates

If you want an accuracy of seven digits, should you then round to that value or simply just cut the numbers after that? Example: 51.1936137567 to 51.1936138 or 51.1936137567 to 51.1936137
177 views

### Difference between datum and ellipsoid for geodetic coordinates?

Looking at the Wikipedia page for the North American Datum, it seems to imply that the datum is completely defined by the ellipsoid, which defines the major/semi-major axes, flattening, etc. For ...
157 views

### How to determine objects area (size) measurement error using satellite images?

I am working at scientific paper about measuring object's size (it's area) using satellite images. I got some progress in it and need to compare my results with other scientific works. I have found ...
226 views

### Queen vs Rook neighborhood

Queen and rook neighborhoods are two common ways to calculate statistics for a focal cell. They are also known an Moore and (von) Neumann neighborhoods. I think a "bishop version", i.e. from lower ...
25 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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### Do locations “move” when shifting datum?

I hope that this is the right Stack Exchange for this question. I may be oversimplifying this, but I'm looking for verification in my understanding of the following: If I have a spatial dataset in 2 ...
102 views

### Digitized Map To Scale

Is it perfectly acceptable to produce a map at a scale of 1:24,000 from a database that was digitized from a 1:100,000 scale source map?
389 views

### What is nontopological geometry?

I need a simple understanding of nontopological geometry. I am completely new in this area so please correct me if I am wrong. As far as I understand in topological geometry the object(say a line) ...
35 views

### Map Projection - Why don't we draw things out

I have been reading about different map projections and kind of understand where the problem lies. And also, most of the problem was that the old cartographers did not have any other tool other than ...
161 views

### How do I find/define a projection that gives me exact relative positions inside an area?

Assuming that a set of positions are all inside a 5km square area: How do I find/define a projection to reproject the positions, so that the relative positions between the now reprojected positions ...
915 views

### Measuring distances when crossing UTM zones?

I like to calculate distance between two UTM coordinates which are in different zones. Could any one point me how I can do this. I found that we can map these coordinates in to a new projection for ...
10k views

### Calculating longitude length in miles?

Suppose I have geographic coordinates of "Saratoga, California, USA" as Latitude: 37°15.8298′ N Longitude: 122° 1.3806′ W I know from here that in case of latitude 1° ≈ 69 miles and that ...
166 views

### Multi-Ring Buffer Methodology

When creating a multi-ring buffer I see two methodologies: Create buffer around feature, buffer the resulting buffer, and repeat for as many rings as required. Using the initial feature to create ...
139 views

### Is there cartographic convention for displaying text label of highest and lowest values in legend?

The first I have found is to have the lowest value and highest value be displayed like the legend shown below (image source) The second is to have relative numbers at the top and bottom (image ...
874 views

### Using GIS tools for non-geographical problems

Many other fields have visual/"spatial" problems that can potentially be solved with GIS tools. I know I've used GIS tools for the odd non-geographical task and was wondering how much this happens and ...
252 views

### Regarding spatial relationships, what is the Dimensionally Extended 9 Intersection Model (DE-9IM)? [duplicate]

In plain English what is the Dimensionally Extended nine-Intersection Model (DE-9IM)? What is the meaning of each row/column in the matrix? How can I use that information to build a relation matrix?...
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### Locating Moon in Sky from Earth

I am working on project which need to find moon location from a specified lat, long on earth. So basically info I am having is Lat,Long and Timezone. Format of the moon location Info? So first in ...
771 views

### Which rule to follow for defining an intersection as an ordered pair of streets?

Explanation Sometimes, for the sake of simplicity or speed, I need to list a location as a pair of intersecting streets. Let's use Luckie Street Grocery Store in Atlanta, Georgia as the example for ...
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### When to use DBMS instead of System Files for Spatial Data Storage?

I'm having trouble deciding when it is best to use a DBMS instead of System Files for storage of Spatial Data. Are there any specific guidelines and reasons for when one method is preferred over the ...
238 views

### Measuring tool shows different measurements for same building in two different map documents?

So I have two map documents with two different Coordinate Systems set for the layers but using copies of the same shapefile. Map 1: Coordinate System: ...
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### Are ellipsoid and datum the same? [duplicate]

Are the datum and the ellipsoid the same? What is a Datum? The Earth is shaped like a flattened sphere. This shape is called an ellipsoid. A datum is a model of the earth that is used in mapping....
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### Internet mapping UX design strategy: Separate desktop and mobile sites, or one site fits all?

I searched GIS.SE for "Desktop vs. Mobile" and didn't get anything helpful, so I guess I'll be the one to ask. Question: With respect to Internet mapping applications, is it better to have separate ...
2k views

### Raster vs Grid vs Lattice terminology?

I have a question about GIS terminology - what is the difference between grid and raster and grid and lattice - in theory?? I thought, that raster is regular network and value is in the cell and the ...
6k views

### Difference between node and vertex in GIS?

In graph theory the term of node and vertex are equivalent, but sometimes in the GIS world the nodes and vertex are mentioned in the same context. I was wondering what the difference is? Node: can ...
196 views

### Can a single raster pixel hold more than one value?

Can a single pixel of a raster hold more than one value?
2k views

### How to calculate the size a bounding box?

What formula could I use to calculate the size in Kilometres of a bounding box based on a given Southwest latitude/longitude and a Northeast latitude/longitude points? The bounding box format is ...
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### Do transfer edges add to the distance cost of a route?

Transfer edges are commonly used in a network dataset to carry a time cost in one direction only (either to-from or from-to). This is fine if the impedance used is time, i.e. find the route that will ...
357 views

### Linear Referencing Methods: Station Equation origins

DEAR PEOPLE FROM THE FUTURE: Here's what we've figured out so far… I am working in the pipelines field, and I get in touch with the concept of the linear referencing methods, specifically with ...
139 views

### Selected Literature on coordinate transformations?

I am looking to hone my skills in the theory and the mathematicas involving the projections systems, projection transformations ( from xy to uv, φλ and vice versa). Can you share the books/pdfs/...
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### Is it better to define object properties or layer properties?

I have a question, but it is difficult to phrase. I am picking up GIS methods as I go, and I have run into this problem frequently. Please excuse me if I am in the wrong place. When organizing ...
153 views

### What are the geometric principles and GIS techniques that I can use to generate a postcode coverage of my city at street scales?

Postal codes of Brazil and another countries are oriented to distribution logistics, and improvement of reliability in writing the postal addresses; but without much concern for the spatial ...