On a map, a closed shape defined by a connected sequence of x,y coordinate pairs, where the first and last coordinate pair are the same and all other pairs are unique.

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2k views

Postgis - Converting 'geometry_dump' data type to a 'geometry' type

I am working with a dataset of property boundaries that has had ST_Union() run on it, thus all the polygons appear as a multi polygon in one row of a table. I would like to separate these out so I get ...
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2answers
2k views

How to smooth large vector polygons from Raster

I have a landuse classification raster file (6 classes) of a large area. But I need it in vector polygons so I vectorised it. No problem so far, but the result is - of course - that every pixel is ...
8
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1answer
278 views

How to automatically reduce polygon size?

I am working with two polygon layers (counties & states) which I will 'intersect' to find which counties are within which states. Due to data inaccuracies I have to change all county polygons and ...
8
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1answer
1k views

Splitting landcover polygons (parcels) into equal sizes, while retaining road access for all?

I would like to split landcover polygons which surround a road polygon into equal sizes, while ALL resulting polygons should have access to the road! Is there any chance to do this automatically? ...
8
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3answers
413 views

Find Duplicate Polygons Algorithm

I have a group of polygons. My objective is to find the duplicate polygons from these group of polygons. Using NetTopologySuite(A c# port of JTS), it is possible to compare two geometires and check ...
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5answers
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How to get an ocean shapefile from a very detailed land area shapefile?

I am looking for a possibility to "invert" a shapefile. What I want to do is to convert a shapefile with the continents and islands into a shapefile that has water polygons. The existing ocean ...
8
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2answers
739 views

Resize polygon along one axis

Using the following example I'm able to resize by scale and origin. polygonFeature.geometry.resize(scale, origin); vectorLayer.redraw(); But does anyone have any suggestions or sample code ...
8
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1answer
145 views

Cutting out the world into polygons of equal population size

I would like to cut out the world into polygons of equal population size, say 100 million persons (starting for example with raster data of population density as provided by the NASA). I know that ...
8
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3answers
1k views

Creating regularly spaced, defined # of points within polygon in QGIS

I used the research tool "Regular Points" to produce a certain number of points within a polygon, but it forms a rectangular grid of points rather than only within the shape of the polygon. Since I ...
7
votes
4answers
6k views

How do I convert a polygon into a point?

I want to convert polygons into points. I know how it's done in ArcGis and I think this may sound trivial but it's a serious issue :/. I'll appreciate any hints :)
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7answers
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Intersection algorithm that correctly handles the 180° meridian and poles?

Is there a well known intersection algorithm that correctly handles 180 meridian and poles? For example, let's say we have a list of latitude and longitude values that represent Antarctica. Let's ...
7
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2answers
1k views

How to remove small “salt & pepper” polygons from a layer?

I have a map made up of multiple polygons, with a few hundred thousand points very small polygons on within it. I need the larger polygons, but not the points small polygons. How do I select and ...
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5answers
2k views

Algorithm to find polygons enclosing points

I'm trying to find an algorithm that can determine the smallest possible polygons to cover a number of points. I know how to get the convex hull around all the points, but say that the points are ...
7
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6answers
3k views

Lines to Polygons

I have failed to find the "name" of the algorithm that would allow one to convert lines to polygons. Since this issues crosses GIS and the fields of computational geometry and computer science. I am ...
7
votes
3answers
3k views

How to insert a GeoJSON polygon into a PostGIS table?

I need to insert a polygon from GeoJSON to my PostGIS table. This is how the SQL query looks like. INSERT INTO tablename (name, polygon) VALUES ( 'Name', ST_GeomFromGeoJSON ( { ...
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votes
2answers
3k views

How to create a heat map or density map from stacked polygons in ArcMap 10

I have a polygon shape file that has many overlapping features. Each feature represents an area used by polar bears. So some of the polygons overlap and some don't, and there are separate clusters of ...
7
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1answer
6k views

How do I change the polygon fill color and border color for SpatialPolygons objects?

I have SpatialPolygons or SpatialPolygonsDataFrames which I'd like to plot. How do I change the color using the three plotting systems in R (base graphics, lattice graphics, and ggplot2)? Example ...
7
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1answer
608 views

How to determine the longest line segment within a polygon that passes through its centroid?

A PhD student approached me recently asking how one would determine the longest straight line that passes through the centroid of a polygon, the output being a polyline rather than just a table of ...
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2answers
355 views

Lossless Polygon Simplification?

Is there a standard/recommended algorithm for simplifying a polygon without shrinking any of its original boundaries? Right now I'm using TopologyPreservingSimplifer within JTS and running into ...
7
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4answers
961 views

Output PostGIS geometry data as centroid or polygon depending on zoom level (GeoServer)

This is what I want: when I zoom out, cities of the country should appear as points and at a certain level when I zoom in, I want them to appear as polygons (showing the area of the city and ...
7
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3answers
637 views

maximum circle inside an irregular polygon from a random point

I am trying to work out an algorithm for creating the maximum radius circle within an irregular polygon (a census tract) based on a given center of the circle. The motivation for this is to obscure ...
7
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3answers
1k views

Create a square grid polygon shapefile with python

i have the following coordinates minx,maxx,miny,maxy = 448262.080078, 450360.750122, 6262492.020081, 6262938.950073 i wish to create a square grid of size 1 m using python. import math ...
7
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1answer
1k views

How to select WFS features by polygon in OpenLayers?

I need to be able to select features on a wfs layer using a polygon instead of a box. I was hoping this would be a standard option in the SelectFeature class. Too bad this isn't the case. Any ...
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2answers
890 views

How to speed up the plotting of polygons in R?

I want to plot the country borders of North America over a raster image depicting some variable and then overlay contours on top of the plot using R. I have been successful in doing this using base ...
7
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1answer
429 views

How to rectify polygon shapes in QGIS?

I have some polygon-shapes in qgis-1.7.0 and want to ensure that every polygon is a rectangle. See image below. Is there any way I can do this in QGIS (or any other f/oss)? Or how can I improve my ...
7
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1answer
944 views

Should I split MultiPolygons into Polygons?

In the system I'm implementing I have a table T1 with an associated geometry. Most of the geometries are a set of n polygons, with 10 < n < 100. At the moment in the table T1 I have a geometry ...
7
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2answers
290 views

How do different GIS systems determine a Polygon's interior?

I'm interested in understanding how real-world GIS systems and their data encode Polygons. Specifically, how do they resolve the ambiguity of a Polygon's interior on a sphere? Background: in 2D, ...
6
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2answers
7k views

How to calculate polygon areas and perimeters using QGIS?

Using QGIS, if I load a polygon layer and make a new column, how do I fill that column with the: area of each polygon and another column with length of the perimeter of each polygon?
6
votes
2answers
270 views

Breaking apart a polygon layer by unique values, creating many new layers

I have a large dataset of habitat information that I need to calculate distances from animal locations to the closest polygon of each habitat type. The way to do this, that I understand, would be to ...
6
votes
4answers
20k views

How to create polygons from lines?

I am trying to create polygons from a line layer of lots and concessions (large blocks of land in rural areas). The lines are mainly grid style as they intersect mostly at right angles. I need to ...
6
votes
4answers
3k views

How to remove only donut holes from polygons using ArcGIS Desktop 10.0?

I have a trick for removing the donut holes, which is converting the polygon to line and then creating polygon out of the lines and in the end merging all of them. The drawback of this strategy is ...
6
votes
2answers
3k views

Converting point sets to polygon boundaries

I'm trying to convert sets of points to their respective polygon boundaries. I think this is something like a Voronoi diagram or Convex Hull, but not quite. I'm sure there's a technical term for it, ...
6
votes
4answers
687 views

Exporting polygon features to individual image pngs

I have a shapefile with a few thousand polygons, ArcGIS [9.3] (and even PostGIS). I would like to export each of those polygons into its own thumbnail image file without any real context. What is the ...
6
votes
1answer
5k views

How to convert a String to OpenLayers.Geometry.Polygon using javascript?

First let me say that I'm using Javascript, jQuery, Java, GeoServer, OpenLayers and PostGIS. Using java class ResultSet I return this String: POLYGON((516000 2135000,515039.264020162 ...
6
votes
1answer
529 views

Filling a polygon with lines using Postgis

i need to calculate a specific distance in an area. The distance is calculated from parallel lines in a polygon, And i need to find out how many parallel lines (with x meters distance to each other) ...
6
votes
2answers
11k views

How to combine adjacent polygons sharing similar trait into single polygon?

I have a large dataset of habitat classes which I have further simplified down into my own unique classes. However, it resulted in there being habitats adjacent to each other with the same forest ...
6
votes
2answers
139 views

summing up over an area based on a distance related function

Through a field study, we learned that the density of a bird species in the forest was related to the distance to forest edge: ln(density) = 1.89*(distance to edge) + 0.34 Now, for any forest ...
6
votes
4answers
308 views

How to avoid holes in polygons from lines?

I am trying to convert a dataset of lines that contains the coast of New Zealand into a big polygon. However using the vector -> geometry tools -> lines to polygon command in Quantum GIS results in a ...
6
votes
1answer
2k views

Polygon label repeated for each tile

I'm using the standalone GeoWebCache to serv tiles from a remote GeoServer. My problem is that the polygon label is added to each one of the tiles served, instead of only once in the polygon centroid. ...
6
votes
3answers
1k views

Can Polygons be generalized to MultiPolygons in GeoDjango?

I set up a model with models.PolygonField in geodjango, using postgres as database. I try to import shp into postgres. The problem is, shp (compiled with QGIS) mixes polygon and multipolygon, hence it ...
6
votes
1answer
690 views

Easily calculate “roundness/compactness” of a polygon

I am trying to find ways to quantitatively describe the shapes of various polygons. For my project, these polygons represent lakes, rivers, lagoons, and parks. So they can be almost any shape. One ...
6
votes
1answer
467 views

QGIS define hexagon area around mapped points

I am using QGIS to map a number of radio antennas (for mobile network). Once I have the layer of the sites (done), I would like to assign to each site a coverage area (envelope). I could achieve that ...
6
votes
1answer
1k views

finding the long axis of an irregular polygon

Hi need some help in how to find the long axis of an irregular shaped ellipse using ArcGIS. I have found the centroid but don't know how to determine the longest distance.
6
votes
1answer
1k views

Where can I find a Unesco World Heritage List as boundaries?

I was wondering if anyone knows where to find the UNESCO world heritage list with boundaries? I can extract point data from the json feed for the map on the website http://whc.unesco.org/en/list via ...
6
votes
2answers
1k views

Finding parcel polygon features with frontage on multiple streets

The Department of Public Works would like to know how many properties in the city have a sidewalk at both the front and back. To get at this, I'm looking for a method to find parcels with frontage on ...
6
votes
1answer
327 views

Efficiently identifying overlapping polygons with Python

I'm parsing the NOAA severe weather alert feed and using it as a datasource for a weather alerting system. In the feed, I occasionally find a polygon entry for an alert. Unfortunately, counties that ...
6
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2answers
4k views

Create a polygon layer from point data

I'm currently using QGIS 1.8.0 I would like to create a polygon layer from a point dataset, where the size of the polygons relates to the resolution of the grid reference. The ultimate aim would be ...
6
votes
2answers
1k views

How to sum pixel values within a polygon zone in QGIS?

I have two layers: a raster layer and a vector layer (polygon). I can see the values of the raster pixels but I don't know how to combine them with information from the polygon layer. More ...
6
votes
1answer
4k views

can I extract overlap of polygons within the same layer?

I am trying to extract the overlap of polygons that are within the same layer in 10. The layer came from a buffered street centerline and I'm trying to extract and delete the intersections from the ...
6
votes
1answer
983 views

Identify polygon overlaps within single shapefile

Using either QGIS (1.9) or ArcInfo (9.3.1) I'm trying to identify unique overlaps of prehistoric building footprints from an archaeological site recorded within a single polygon shapefile. While the ...