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

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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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1answer
46 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
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1answer
101 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 ...
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2answers
84 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 ...
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0answers
61 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 ...
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0answers
19 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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0answers
45 views

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 ...
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1answer
62 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?
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2answers
177 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) ...
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1answer
33 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 ...
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1answer
155 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 ...
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1answer
506 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 ...
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1answer
139 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 ...
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2answers
104 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 ...
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3answers
799 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 ...
2
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1answer
168 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 ...
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1answer
48 views

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 ...
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3answers
459 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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0answers
126 views

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 ...
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2answers
188 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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0answers
41 views

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 ...
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0answers
72 views

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 ...
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1answer
1k 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 ...
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4answers
5k 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 ...
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3answers
167 views

Can a single raster pixel hold more than one value?

Can a single pixel of a raster hold more than one value?
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1answer
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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1answer
65 views

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 ...
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0answers
317 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 ...
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4answers
137 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 ...
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1answer
38 views

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 ...
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1answer
150 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 ...
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1answer
253 views

How to store route names of a stop belonging to multiple routes

I've been reading the ArcGIS help files on route analysis to gather more information on what attributes are stored with Stops. Maybe I've stared at the screen too long, but I cannot seem to understand ...
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3answers
374 views

Does Earth's magnetic field affect any datum definition?

I had an interview last week. One very interesting question was "does earth's magnetic field affect any datum definition?" I was sure it does not for geocentric datums. But I thought maybe the ...
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1answer
4k views

Polygon Centroid Options and Appropriateness (FeatureToPoint, Labels, etc)?

I've found a couple of other Stack Exchange questions related to this, but they were not satisfying. For example: How does ArcGIS Desktop calculate INSIDE point for Feature to Point? does not tell ...
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7answers
2k views

Spatial reference for dummies?

Can anyone recommend a good reference or tutorial that explains the principles of spatial references, projections, and coordinate systems? We are a small team of programmers working with GIS ...
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3answers
10k views

How do you compute the earth's radius at a given geodetic latitude?

(I see there is an equation on wikipedia that does exactly what I am asking but there is no references. I have no way of confirming the validity of this equation!) I already understand the difference ...
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2answers
25k views

Differences between triangulation and trilateration?

Looking around I noticed that many people interchange the terms (triangulation and trilateration) for the same sense. What is the correct sense of Triangulation and what are the differences from ...
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4answers
1k views

Recommend topics to be included in a Computer Science for Geospatial Technologies course

I will be instructing a course at the local university titled Computer Science for Geospatial Technologies. This is an introductory course meant to introduce computer science concepts to geospatial ...
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1answer
122 views

How can I generate a range of pantones for a map?

When I am given a map (or make one...) I often like to get an idea of the range of colours present. One thing this does is it allows me to quickly visualize contrast (helps build maps for colour blind ...
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0answers
257 views

Topology - To be, or not to be, that is the question [closed]

Topology, I mean "real" topology, is not a new concept and it's available since a long time in GRASS gis. I won't speculate the reasons myself but, after a long period of spaghetti model ...
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1answer
726 views

Is there cartographic convention to ordering legend items (high-low or low-high)?

When you symbolise a layer in ArcMap, the symbols are ordered from low value to high value by default. Is that necessarily "correct"? I've never officially studied cartography - is there a convention ...
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3answers
179 views

Understanding location storage and query algorithms?

One of the most important aspects of a GIS-equipped database is that it provides the user with the capability to quickly query for all points within some arbitrary geographic area that match some ...
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1answer
887 views

Error assessment of calculation done using unprojected vs. projected data

This question builds off of the one with the subject line "Calculating Flow Direction and Delineating Basins from Projected vs. Unprojected Data.": Calculating Flow Direction and Delineating Basins ...
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1answer
5k views

Calculating Flow Direction and Delineating Basins from Projected vs. Unprojected DEM Data

This is somewhat of a theoretical question stemming from some discussions with colleagues on the topic of implications with delineating basins with projected (e.g., Albers Equal Area) vs. unprojected ...
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4answers
1k views

Calculating visible sky percentage?

Can anyone explain, as simply as possible, how to calculate the visible sky percentage? I have done a satellite survey and have worked out the height of buildings and the distance between them. ...
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3answers
382 views

How can Flocking Algorithms be used in GIS?

The first flocking algorithm was written by Craig Reynolds in 1986. A recent browser implementation can be found here. ...
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3answers
1k views

Is the Fourth Dimension used in GIS?

Whilst working with OGR, I came across the following field used define a geographic dataset: COORD_DIMENSION The spatial dimension (2, 3 or 4 dimensional) of the column. Whilst I've used 2D and 3D ...
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6answers
5k views

Algorithms for matching segments

What are the best algorithms to match segments? I'm trying to match corresponding segments from two map sources, one less accurate but with segment names, and one more accurate without segment names. ...
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1answer
3k views

How to create an accurate Tissot Indicatrix?

A Tissot Indicatrix is useful method for communicating at a glance the kinds of distortion a given projection is prone to (in the figure below, each of the red circles occupies the same area). I've ...
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54answers
60k views

What Makes a Map Beautiful? [closed]

Often times when we make maps it is based on our subjective interpretation of what is aesthetically pleasing. I would like if people posted examples of beautiful maps, displaying any phenomena in any ...