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Questions tagged [gis]

A Geographic Information System (GIS) captures, stores, analyzes, manages, and presents data that are linked to location(s). The GIS Stack Exchange should be considered for questions with this tag.

According to Wikipedia:

A geographic information system (GIS), geographical information system, or geospatial information system is any system that captures, stores, analyzes, manages, and presents data that are linked to location(s). In the simplest terms, GIS is the merging of cartography, statistical analysis, and database technology.

There is a Stack Exchange site devoted to Geographic Information Systems.

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Fastest Way to Find Distance Between Two Lat/Long Points

I currently have just under a million locations in a mysql database all with longitude and latitude information. I am trying to find the distance between one point and many other points via a query. It's not as fast as I want it to be especially…
Ryan Detzel
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Preferred order of writing latitude & longitude tuples in GIS services

When dealing with GIS source code you often need to write latitude and longitude coordinate tuples. E.g. in Google Maps links (123,…
Mikko Ohtamaa
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Get lat/long given current point, distance and bearing

Given an existing point in lat/long, distance in (in KM) and bearing (in degrees converted to radians), I would like to calculate the new lat/long. This site crops up over and over again, but I just can't get the formula to work for me. The…
David M
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3 answers

Difference between GeoJSON and TopoJSON

What is the difference between GeoJSON and TopoJSON and when would I use one over the other? The description of TopoJSON on GitHub implies the TopoJSON files are 80% smaller. So why not just use TopoJSON all the time?
Luke
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5 answers

GIS: PostGIS/PostgreSQL vs. MySql vs. SQL Server?

EDIT: I have been using Postgres with PostGIS for a few months now, and I am satisfied. I need to analyze a few million geocoded records, each of which will have latitude and longitude. These records include data of at least three different types,…
Aren Cambre
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7 answers

Best way to overlay an ESRI shapefile on google maps?

What is the best way to overlay a shapefile in Google Maps? After some reading suggests that, converting shapefile into KML and overlaying KML in Google map is an option. If that is the case, how do I convert a shapefile into KMLs? I believe there…
Carsen
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Convert a shapefile (.shp) to xml/json

I'm working with a shapefile (.shp, .dbf, etc) and would like to convert it to xml. I'm on a mac, and I'm having trouble finding an application that will help me with the conversion. Does anyone know of a method for converting this file format into…
minimalpop
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Is there an efficient algorithm to generate a 2D concave hull?

Having a set of (2D) points from a GIS file (a city map), I need to generate the polygon that defines the 'contour' for that map (its boundary). Its input parameters would be the points set and a 'maximum edge length'. It would then output the…
Fabio Ceconello
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Loading a local .kml file using google maps?

I created a hello world program to load a local kml file (borrowed from google's docs): var ctaLayer = new google.maps.KmlLayer("http://localhost:8080/kml/cta.kml"); This does not work (nothing gets loaded). However, when I change that line to: …
hddd
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Fast Haversine Approximation (Python/Pandas)

Each row in a Pandas dataframe contains lat/lng coordinates of 2 points. Using the Python code below, calculating the distances between these 2 points for many (millions) of rows takes a very long time! Considering that the 2 points are under 50…
Nyxynyx
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Determine timezone from latitude/longitude without using web services like Geonames.org

is there any possibility to determine the timezone of point (lat/lon) without using webservices? Geonames.org is not stable enough for me to use :( I need this to work in PHP. Thanks
Jacek Francuz
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7 answers

How to intelligently degrade or smooth GIS data (simplifying polygons)?

I have detailed US county maps, from the TIGER LINE data sets. How might I sample, smooth, or degrade the data so that I get straighter, more boxy, less "noisy" shapes to represent the geographical features -- in this case just county boundaries and…
unmounted
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Google maps: place number in marker?

How can I display a number in the marker on a google map? I want to do server side clustering and I need to display how many points the cluster represents.
User
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2 answers

What is ST in PostGIS?

Almost all the functions in PostGIS start with ST. e.g. ST_Distance_Sphere, ST_GeomFromText, ST_Intersection, etc. What does ST mean? http://www.postgis.org/documentation/manual-svn/PostGIS_Special_Functions_Index.html
hekevintran
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4 answers

How to Convert data frame to spatial coordinates

I have been working on earthquake data that has lat long values, and I want to convert those lat long values to spatial coordinates. Suppose I have the following data set df: longitude latitude 128.6979 -7.4197 153.0046 …
mk04
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