Measure of quantity of a two-dimensional surface
0
votes
2answers
24 views
How to scale/reduce my polygon without changing the central lat & long?
I am writing a VBA code to resize my polygon, I get a input as vector points(Shape file). The code below resizes it as according to my scale factor but my central latitude and longitude are also ...
2
votes
1answer
53 views
How does QGIS calculate the area of a polygon?
I am working on a project that requires the calculation of the area of a polygon by two different methods. I need to know what algorithm QGIS uses to calculate the area of a polygon. I know ESRI ...
1
vote
0answers
57 views
How calculate areas between certain contour lines in qgis?
Sorry for asking a question which I found in similar ways already here, but I am trying this for days and just got no result:
How do I calculate the area between certain contour lines (e.g. 0-800, ...
2
votes
1answer
90 views
How to calculate volume from a raster file?
I have a raster file containing the depth of water. I need to find the volume of water using that raster file. I need to find the area of each cell and multiply with the depth. How can I do it in ...
3
votes
2answers
67 views
How to calculate the shared area between a raster and a shape file in ArcGIS 10?
I have a raster file with 5 classifications developed from habitat modelling algorithms. I'd like to know how much of 2 classes of the raster is covered by the network of protected areas (Shape file). ...
3
votes
1answer
45 views
How to exclude some parts of raster classes based on size of area?
I have a raster file with 5 classifications. I've calculated area for all of the classes via Zonal geometry, Arcmap 10. Now, I want to exclude patches which are smaller than 100 sq. km. and ...
1
vote
1answer
46 views
Calculating area
I have a polygon layer.
I toggled to edit mode.
I added a new column, while number (integer) and called it "area".
I then use the field calculator - geometry - $area to populate the polygon area for ...
2
votes
1answer
157 views
What are the units of the calculated area from a raster in decimal degree
I'm trying to calculate area for a raster file which contains 2 layers (0 for unsuitable habitat and 1 for suitable). It's been calculated successfully but I don't know what is the unit of the ...
3
votes
1answer
69 views
Compute global DEM topographic indices and compromise projections
I would like to compute global topographic indices based on SRTM elevation data. These indices are computed along river/channel networks extracted from a DEM and are a functions of both local slope ...
2
votes
1answer
78 views
ArcGIS - merge polygons and get combined area
I cannot for the love of god figure out how to combine (join?) two overlapping polygons to determine the combined area they cover in ArcGIS 10. I am sure the Geoprocessing tools can do it, but just ...
2
votes
2answers
97 views
How to calculate area in sq km of an ellipsoid shapefile
In QGIS, I often find myself setting up projects with an ellipsoid coordinate system (e.g. WGS84) so that the resulting maps have lat lon scales, etc.
Often in these projects I also need to do some ...
2
votes
0answers
62 views
Raster area (QGIS) problem explained
I would like to know the area that each value in a raster has... The raster I have has values from 2-15 and I would like to know the area that each value is occupaying within my polygon... Thanks!
I ...
3
votes
1answer
165 views
Calculate area within Python script in Arcmap
I am trying to calculate the area of a polygon within my Python script. I create a new polygon from merging two together, and I'd like to add the area of the resulting polygon to a field in the output ...
0
votes
2answers
99 views
Calculating area gets a different result
I've calculated the area of polygons with QGIS by using ctr-i - geometry - $area. I've set it on real. The results seem fine, but I've noticed they differ from the area given when I use the ...
2
votes
1answer
92 views
How to measure the area of polygons within a fishnet
I am currently trying to measure the area of polygons within each square of a fishnet. The aim of what I am doing is to work out the proportion of different agri-environment schemes by 1km squares. ...
1
vote
1answer
37 views
QGIS 1.8.0 Mac where is measure window or measure area symbol?
Just trying to measure the area of a selected polygon (a few km2) but can't find out where the measure symbol is (mentioned in some posts here) or how to get the measure window shown in the manual. ...
0
votes
0answers
11 views
Assigning an area to a geoprocessed polygon [duplicate]
using QGIS
I've geoprocessed a layer using the difference function but the newly created layer still holds the area attributes of the layer I used as the input layer...
ie on my output layer, a tiny ...
2
votes
2answers
141 views
How to calculate the area of rasters in QGIS?
I have been working with some rasters and would like to know how to calculate the area occupied by one element of a raster in Qgis.
1
vote
1answer
340 views
Calculate polygon area inside extent
We're using ArcMap 10.0 sp5, creating a tool in c# using the ArcObjects sdk.
Is there a built in function or simple set of steps that calculates the area of each feature of a polygon layer within a ...
0
votes
0answers
74 views
SqlGeography STArea for CW and CCW polygons
I'm using a SqlGeographyBuilder to make a simple polygon (with SRID of WGS84). When I add the vertices CW and call the STArea() method, The area would be very large. When I add the vertices CCW and ...
4
votes
1answer
130 views
The number of digit of decimal point when you calculate area of polygon in QGIS1.8.0
I would like to change the number of digit of decimal point when I calculate area.
For example
Now: 32.456677
Ideal: 32.46
I try to adjust "output field width" and "Precision"
These don't work well.
...
3
votes
3answers
193 views
Auto-calculate field (area or formula)
I'm wondering if anyone has any insight into the potential to auto-calculate the value of a field, either area or distance (ideally) or a formula (based on the values of say 2 other fields, or an ...
3
votes
0answers
159 views
Polygonize vegetation area from Landsat7 RGB using QGis / Bilko?
I'm trying to extract the areas with vegetation as a polygon-shape from a landsat7-image, 30m resolution, RGB, using QGis 1.8 or Bilko or (hopefully in the near future) ArcGIS. The area is in Northern ...
0
votes
1answer
147 views
Which area measurement to trust? - The same polygon in GoogleEarth v. ArcGIS [duplicate]
Possible Duplicate:
What is the most accurate coordinate system for calculating areas of polygons?
I'm currently involved in comparing the "official metropolitan" areas of several cities ...
6
votes
1answer
186 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 ...
1
vote
1answer
275 views
How to use field calculator for area calculations in QGis? [duplicate]
Possible Duplicate:
Calculate area between contour lines on a DEM with Qgis 1.8.0-Lisboa
Based on a DEM of a whole country I have reclassified altitudinal bands with steps of 100 metres ...
3
votes
1answer
75 views
PostGIS: worldwide area calculation
I have a table with polygons in EPSG 4326. These polygons are distributed all over the world, for example:
POLYGON((10.7324632658845 59.9253049236956,10.7331908150806 ...
6
votes
3answers
318 views
How do I get the area of a WGS84 polygon in square meters?
The following gives me the area of the polygon in square degrees:
SELECT ST_Area(ST_GeomFromText('POLYGON((871325.790874952 6105405.3261047,871418.748307692 6105359.72944624,871346.22022442 ...
6
votes
1answer
338 views
How to calculate te area between contour lines on a DEM with Qgis 1.8?
Does anyone know how to calculate the area in km² for each altitudinal band (between 100 and 200, 200 and 300...) based on a DEM? I added the contour lines with a distance of 100 metres but could not ...
1
vote
0answers
22 views
area weighted average for overlapping polygons [duplicate]
Possible Duplicate:
How to use NASS county level crop data to estimate crop acreage in hydrologic regions?
It seems like an easy problem but I don't know how to go about it.
I have two ...
5
votes
2answers
559 views
How to split an irregular polygon into equal areas?
I am a surveyor and use QGIS for maintaining soil test records on civil projects and am constantly provided with test lot area or number of lots required. These are more often than not irregular in ...
3
votes
2answers
107 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 ...
6
votes
1answer
124 views
How do I represent the whole Earth as a Polygon?
This is related to determining the interior of a Polygon.
My difficulty is that if I specify a Polygon covering the Earth going from East to West, it will still have a boundary along the ...
6
votes
2answers
151 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, ...
1
vote
1answer
88 views
Transform csv-coordinates into area
I'm working with an inventory of a species in Southern Sweden. I have recorded my findings (together with coordinates, name of the species and year of finding) and created a CSV-file with i have ...
4
votes
4answers
208 views
How to compute geodesic area in GeoDjango?
I have some polygons which can be anywhere in the world. I would like to compute their areas.
The GeoDjango docs for GEOSGeometry.area don't specify whether it is geometric or geodesic area, but ...
5
votes
2answers
158 views
PostGIS - area-weighted calculation on an intersection
I'm trying to learn postgis sql by performing some familiar operations from ArcGIS. Here, I want to perform an area-weighted calculation of certain populations on the intersection of a set of parcels ...
6
votes
2answers
274 views
calculate area of vegetations in a raster file
How do I calculate area of several vegetation types in a raster (.img file type) image. They are color coded. Am using QGIS (1.8.0) and ERDAS 9.2.
6
votes
2answers
251 views
How to get correct area calculation using Google Mercator?
i use QGIS with openlayers-plugin and i´ve loaded google satellite as a layer. what i want to do is making a shape-layer (polygon) with the goal to get the area values of the polygons. i´ve activated ...
5
votes
1answer
459 views
How to measure area correctly?
I have now used my entire evening, but I can't figure out how to make areal calculations (eg. in km2). I have tried the 'field calculator', I have tried the 'measure area' function on the "attributes" ...
2
votes
2answers
209 views
How to single out country data from a world data map?
Say that i have two "data sources";
A global map of average wind speeds,
A shape file (or similar information) of all country borders in the world.
How do i combine these two sources and extract ...
1
vote
1answer
101 views
Summarize polygon area using another polygon
I have a shapefile representing public/private lands in Montana. This is a multipart shapefile where I've simplified attributes so that #1==private and #0==public.
Next I have a shapefile of ...
1
vote
1answer
184 views
ESRI android SDK Calculate area in square meters from polygon geometry
Hello I have a Polygon object in ESRI Android SDK that I'm creating on a map, I would like to calculate that polygon object to square meters.
currently I use
double area=polygon.calculateArea2D();
...
3
votes
1answer
303 views
How can I get my Qgis area calculations in metres rather than degrees? My shapefiles are projected using WGS 1984 UTM fuseau 35 Sud
I am using Qgis 1.7.4 to calculate the area of polygons. My shapefiles have been projected using the coordinate system WGS 1984 UTM fuseau 35 Sud, but my area calculations are still displayed in ...
2
votes
0answers
67 views
GeoTools, add column in query with CQL
I'm trying to query the database (DataStore) and want to let the datastore calculate a value for me.
In SQL I would do it like this:
SELECT name, ST_Area(ST_Intersection(the_geom, ....) AS myValue ...
2
votes
0answers
436 views
How to calculate the area of a polygon considering the relief?
I work in a fire department and i'm mapping all the fires that occur in my area, creating polygons that represent burnt areas.
my problem is that the values are not accurate... for instance, arcgis ...
3
votes
1answer
192 views
How to calculate buffer surface that falls within another layer's borders
The image below shows what two selected layers. One contains a series of borders, and the other a series of buffers.
I am trying to obtain the buffered surface within each of the borders in the ...
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?
4
votes
2answers
294 views
How to calculate area of 1 x 1 degree cells in a raster
I have a simple array (not geo-referenced in any way) in Matlab (which is not a language I know a huge amount about...so I can export it to other languages if needed) which has the dimensions 180 x ...
4
votes
2answers
410 views
Why does ST_Area(g.geom) + ST_Area(p.geom) - ST_Area(ST_Union(g.geom,p.geom)) produce negative result when using ST_Overlaps(g.geom, p.geom) = true?
I have two set of shape data. Let's say file gov.shp contains list of post codes and their boundaries. File post.shp contains list of government area name and their boundaries. I want to find out the ...
