# Tagged Questions

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

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### 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 ...
43 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 ...
48 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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### 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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### 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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### 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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### 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 ...
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### 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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### 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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### 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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### 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 ...
510 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 ...
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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### 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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### 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 ...
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### 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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### 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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### 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 ...
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### 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 ...
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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 ...
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 ...
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 ...
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### 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 ...
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### Linear Referencing Methods: Station Equation origins

DEAR PEOPLE FROM THE FUTURE: Here's what we've figured out so farâ€¦ 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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### 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, Ď†Î» and vice versa). Can you share the ...
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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 ...
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### 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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### 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 ...
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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### 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 ...
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 ...
11k 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 ...
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 ...
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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### 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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### 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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### 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 ...
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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### 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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### 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 ...
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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### 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. ...
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 ...