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.
16
votes
4answers
3k views
Separate polygons based on intersection using PostGIS
I have a PostGIS table of polygons where some intersect with one another. This is what I'm trying to do:
For a given polygon selected by id, give me all of the polygons that intersect. Basically, ...
19
votes
7answers
8k views
Removing small spaces between polygons
I have a set of polygons representing administrative districts. The districts were digitized by hand, and there are small spaces between polygons where the polygons should be touching. How can I ...
16
votes
3answers
805 views
Packing Polygons within polygon
I have a Boolean raster.
In the grey areas of the raster I would like to fit a given size polygon within a contiguous extent.
Basically, I have an irregular polygon, and i would like to "fit" a ...
16
votes
3answers
2k views
How can I calculate the average width of a polygon?
I'm interested in examining the average width of a polygon that represents the road surface. I also have the road centerline as a vector (which is sometimes not exactly in the center). In this example ...
7
votes
6answers
2k 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 ...
8
votes
3answers
6k views
How to convert .shp to .csv including attributes AND geometry?
I have a .shp file with 60k+ entries, all of which are polygons with corresponding attributes (acreage totals, landowner names, tax ID #s, etc.). What I ultimately need is a .csv file with all of ...
7
votes
2answers
904 views
How to check Topology in QGIS?
I have two Shapefiles with Polygons ( City and Forerst)
Is there a Plugin who is able check the topology (QGIS)? Like "Knots do not overlap" or something like that? I dont want that they overlap.
...
3
votes
0answers
174 views
How to estimate the average width of a sidewalk? [duplicate]
I have a table with two polygons representing urban block with and without the sidewalk: geomBlock and geomBlockWithSidewalk.
On my city we can approximate the polygons of geomBlockWithSidewalk to a ...
4
votes
1answer
262 views
Identify Polygons on raster image
I have OS street view mapping as raster images. Is it possible (without the obvious of tracing each dwelling) to identify all polygons on each tile.
To clarify,
My ultimate aim is to produce a ...
10
votes
3answers
1k views
Optimizing a nearest neighbor calculation using PostGIS
I'm using PostGIS to calculate the nearest neighbors of polygons. What I want to calculate is the minimum distance from each polygon, to the nearest polygon.
Thus far I have got great help from Mike ...
12
votes
5answers
3k views
Generate points that lie inside polygon
I have polygon feature and want to be able to generate points inside it. I need this for one classification task.
Generating random points until one is inside the polygon wouldn't work because it's ...
10
votes
3answers
210 views
How to improve drawn shapes in Quantum-GIS?
I have a polygon-shape in qgis-1.7.0 and want to fix overlays and gaps between the edges of adjacent polygons. See image below.
Is there any automated way to do this in quantum-gis? Or any other ...
6
votes
1answer
312 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) ...
8
votes
4answers
2k views
How to find the minimum edge to edge distance of polygons?
I have a a map of about 3000 polygons in ArcGIS 10. I'm looking to find the distance between each one of them. I know how to do it using the lat and long coordinates of the centroid, but I'm looking ...
4
votes
3answers
83 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
(
{
...
4
votes
1answer
257 views
What is the best way to connect spatial data with attributes in Excel table?
I have many attributes which are stored in an Excel table. They refer to USA counties. I need to somehow connect those attributes to polygons in some format (don't know which is the best) and ...
7
votes
1answer
1k views
Instantiating spatial polygon without using a shape file in R
So, the usual way we read a shapefile in R is via the maptools package, like this:
sfdata <- readShapeSpatial("/path/to/my/shapefile.shp", proj4string=CRS("+proj=longlat"))
However, I have a use ...
6
votes
1answer
192 views
How to draw shapes with highest possible decimal accuracy
I am trying to read input of lat and long to draw the shape based on condition.The input is standard array of lat and long with 15 decimal accuracy. I am realizing - I am loosing some decimal accuracy ...
4
votes
1answer
869 views
Create overlapping polygons from contour lines
Working in ArcGIS 10, I have a set of contour lines representing density of commercial square footage, and I have a set of points representing local maxima for each peak of the dataset. For each ...
3
votes
2answers
629 views
How to edit Shapefile Attributes?
How might I go about exporting a polygon shapefile (e.g. CSV) so that attributes (not geometry) are editable by others, and importing it with the changed attributes (of which there are several columns ...
2
votes
1answer
123 views
find polygon corner coordinates
I am trying to get the coordinates of each node of the polygon I create. I would like the attribute table to display the name of the polygon (ex. address) and then the coordinates of the nodes (ex. ...
1
vote
1answer
405 views
Unproject Radius with Openlayers with CRS:84 Projection
I have made a Openlayers integrated map that lets you draw a circle, On completion of the circle I have told the map to give me , Bounds, Center Long and Lats, and lastly the radius. My problem is ...
14
votes
2answers
2k views
How can I find a point inside a polygon in PostGIS?
How can I find a point that is guaranteed to be within a given polygon in PostGIS?
I am aware of the ST_Centroid function. However, the centroid is not always within a polygon, see below:
...
6
votes
5answers
1k 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 ...
3
votes
0answers
116 views
Area-weighted rasterising of polygon data
I'm looking for any GIS tool to do detailed rasterising of polygons. I've checked GDAL's gdal_rasterize command (and API), and ArcGIS's Polygon to Raster tool, but they only rasterise 1 attribute per ...
5
votes
3answers
363 views
How do I use polygons to apply a unique value to all raster cells within those polygons?
In ArcGIS 9.3, I have a raster file that I would like to "mask" with polygons, giving a single value to all the raster cells that overlap the polygons. How can I do this? Here's a screen shot, where ...
11
votes
5answers
3k views
How to use ST_Intersection?
Here's a quick summary about what I'm trying to do: I have 3 tables in Postgres, 'a' and 'b', each have a Polygon column, and 'c' has a Point column. What I'm trying to do here is to get the ...
7
votes
5answers
367 views
Where can I get neighborhood boundaries?
Besides Zillow's creative-commons licensed neighborhood boundaries shapefiles, what sources of neighborhood boundaries are there? Not just in the US, but all over the world.
Free/open source is ...
7
votes
4answers
8k views
Extract coordinates of polygon vertices in ArcMap 10?
I've got about a dozen polygons in a feature class loaded in ArcMap 10, all in geographic WGS 1984.
How do I easily obtain the coordinates associated with each vertex of each polygon in that feature ...
3
votes
3answers
296 views
Selecting polygons with a minimum internal straight line value - ArcGIS 10
I have a map of polygons representing forest stands. I am trying to sort through them to find those polygons that have a minimum internal distance of 200 m in a straight line (my field sampling will ...
0
votes
1answer
2k views
Openlayers get coordinates of a circle vector after draw
I have made a openlayers map. I have made two features on the map.
Navigate
DRAW POLYGON
I have made 40 sides to my polygon which turns out to be a circle.
After I have drawn my circle I want to ...
13
votes
2answers
982 views
How can I fix my complex Polygons so they show correctly in Google Maps?
Problem: I'm trying to find a way to fix some broken polygon shapes and I'm not sure how I can do this.
Details:
I've got a number of polygons which I basically imported from TIGERLINES a while ...
9
votes
6answers
1k views
How to find the boundary co-ordinates from a given set of co-ordinates
Given a set of coordinates, How do we find the boundary coordinates.
<== Figure 1
Given the coordinates in the above set, How can I get the coordinates on the red boundary. Boundary is the polygon ...
5
votes
2answers
273 views
How to enclose clustered points with polygon?
I have a raster with forest (1), no forest (2) data. "1" is represent single/few trees and there is gaps between them. I want to create a polygon around these trees to a forest map. It is not a dense ...
5
votes
1answer
165 views
algorithm for displaying holes in a polygon by translating it into several hole-less polygons?
I'd like to plot polygons with holes on a framework that doesn't support holes. The approach to me seems to be to translate the single polygon into several ones adding up to the whole polygon, leaving ...
5
votes
3answers
248 views
Selecting polygons by number of sides
I'm using ArcGIS 10 to build some figures for a journal article. One is a figure of an unstructured finite element mesh of triangles spanning the western Atlantic Ocean. I exported this mesh from ...
4
votes
1answer
2k views
Arcgis 10: Point layer, polygon line layer, draw points to the nearest polygon point or other nearest line?
I have been using arcGIS for a while now but I often get frustrated with it :(
I have version 10.0 arcGIS and I'm have two layers
1) Point data (building locations)
2) a polygon shape file (outline ...
4
votes
3answers
538 views
How to split features?
I would like to split a shapefile in qgis according to how the polygons overlaps. Don't know how to though? See pic for explanation:
4
votes
2answers
2k views
How to calculate polygon areas and perimeters?
If I load a polygon layer and make a new column, how do I fill that column with the 1) area of each polygon and another column with 2) the length of the perimeter of each polygon?
3
votes
2answers
102 views
Determine density or cover from a raster layer that has been clipped by a polygon
I am a very new GIS user using ArcMap 10. I have a raster layer of tree canopy that I have clipped so that the layer is in a polygon that is a circle with a 2km radius.
I have done this for four ...
3
votes
0answers
126 views
Rgeos drops associated values when intersecting polygons
I am trying to intersect two SpatialPolygonsDataFrames and get a SpatialPolygonsDataFrame as the result. Unfortunately, using the gIntersection function from rgeos (which works impressively quickly ...
3
votes
1answer
204 views
QGIS Polygon layer table of adjacent polygons
In a polygon layer, how can I generate a table of adjacent polygons?
3
votes
2answers
445 views
Merging polygons that intersect by more than a specified amount
I am working with a dataset that contains a subset of property boundaries in a local government area, thus my dataset is made up of several thousand properties but not all are touching. Since it is a ...
3
votes
2answers
4k views
Cannot get areas for polygon layers in ArcMap 10
For an ArcGIS project opened in ArcMap 10, we have added polygon layers representing different geographical features.
After all the polygons were created, we opened the attribute tables for those ...
2
votes
2answers
644 views
How to change the vertex style for editing?
When I use drag feature, then the circles on the polygon edge has the same style.
For example, this OpenLayers site.
I need to change it, I mean they need to be a different color.
What is their ...
0
votes
3answers
3k views
Understanding the polygon handler function in Openlayers
Using openlayers, I want to be able to draw one polygon on a map. After one polygon is drawn, I want an event to fire that stops any more from being drawn until a button is pressed. My current code ...
6
votes
2answers
1k 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 ...
5
votes
3answers
1k views
Why doesn't the split tool return any records in the attribute table?
I've been trying to split a large land use shapefile using a set of study area polygons as the split feature, but when the function finally finishes running (the land use dataset is quite large), all ...
4
votes
1answer
421 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.
4
votes
2answers
1k views
Removing sliver polygons, ArcGIS 10
I unioned 2 layers into 1 layer, and it created sliver polygons.
I used the elimination tool to merge them with neighboring polygons.
As as result, it merges all sliver polygons to only one polygon ...
