0
votes
0answers
22 views

How to calculate the area of an ellipse on the earth's surface using Python?

I have a dataset consisting of GPS coordinates. I use a clustering algorithm to generate a two dimensional Gaussian for me. The Gaussian takes the shape of an ellipse if visualized on the map. ...
5
votes
2answers
125 views

How to calculate the area between two line shapes?

I'm a newbie using QGIS (2.0). I'm trying to calculate the sidewalk area of a city. For that I have some shapes, extracted from Mricostation, with the topology (facades, fords, fences, etc.), but ...
0
votes
0answers
20 views

Show the paths but not roadsides and driveways in the line layer

I want to display paths in the woods but the paths are all in One (line) layer that contains all roadsides, pavements, drivvays, but also paths, tractor road and other relevant roads in, and up to the ...
0
votes
0answers
57 views

changing unit of area from unknown unit to square meters

I am using Qgis 1.8 and I have this polygon.Now I wanted to know the area of this polygon and i have used field calculator and it shows my area as 651692439.under general tab crs is : EPSG:4326 - WGS ...
0
votes
2answers
68 views

Show only some buildings

How do I show only some buildings? I only need to show 3 cabins in the forrest, but not every house in the whole village around, and the city close by. Maybe some of the symbol buildings in the city ...
3
votes
1answer
148 views

Can't compute area of shapefile in field calculator

This shapefile represents the counties of NM. I am trying to compute the area of each polygon (yes, I know there is an area field, but this is a simpler example of a problem I'm having which doesn't ...
1
vote
2answers
79 views

how to identify qgsvectorlayer area?

I need to identify the area from Qgis qgsvectorlayer anyone have an idea how to do that in python ?
4
votes
1answer
73 views

Area calculation of an object without coordinates

I have a photo of an object with a scale and I want to calculate its area. I guess I have to create a polygon of the area to be calculated to use the 'field calculator'. But how do I tell the program ...
2
votes
1answer
73 views

Unable to change the layer unit in QGIS

I have been working with QGIS for 2 weeks and I got the hang of it now. The problem now is I cannot calculate the area of a created polygon. Because the layer unit is not changing to meters. When ...
1
vote
1answer
140 views

Visualise data belonging to an area

I am looking for a way in QGIS (1.8.0) to visualise data, which is related to an area (polygon on a shape file). There are no x-y-coordinates with the data, just the info of the belonging area, means ...
2
votes
2answers
177 views

Is the derived area/length/xy values of a polygon/polyline layer in QGIS usable?

I have a raster that is projected to a state plane CRS and I am adding polygon/polyline shapefiles that are projected to WGS84. On the fly transformation is set to reproject to my raster CRS. When I ...
4
votes
1answer
140 views

How can I accurately measure area of polygons using field calculator in qgis?

I have several polygon shapefiles, both set to WGS84 CRS. I have been using the google basemap with the Openlayers plugin, using the mercator CRS. On the fly CRS transformation is enabled. Should ...
1
vote
0answers
52 views

How to measure area of polygons generated from gps data in qgis? [duplicate]

Somebody classified my question as a duplicate. But applying the answer doesn't work for me. Here is what I did: - I made sure that my layer is in a projected coordinate system (UTM30N, WGS84) - I ...
1
vote
1answer
158 views

How to compute area for polygons in an EPSG:4326 shapefile?

I have a shapefile covering the whole globe, in EPSG:4326 (geodetic WGS84). I would need to compute the polygons areas in a metric such as km2. How can I do that in QGIS or with gdal/ogr and having a ...
0
votes
4answers
143 views

How can I calculate different polygons by different attributes?

I'm doing my master thesis and want to calculate different polygons (in QGIS 1.8 for Mac) in four different columns which I defined by different attributes. i.e. some of the attributes in the first ...
1
vote
0answers
23 views

Creating a buffer based on area (i.e. sqm) instead of distance [duplicate]

Is there a way in ArcGIS 10.1 or QGIS (or any add-on) to create buffer based on an area (i.e. sqm) rather than using buffer distance? I'd like to create a buffer of let's say 5% of the area within the ...
1
vote
2answers
170 views

How to re-calculate area, perim, p2a,width and length in QGIS?

I cut a part out of one feature and added it to another feature in a polygon shapefile. My problem now is that both features has the same values in the area-, perim-, p2a-, width- and length-columns? ...
0
votes
1answer
141 views

How to calculate the area of the convex hull of a points layer

I have a shapefile in QGIS that I have created by importing a CSV of points, using Points2One to convert to a shapefile and then importing the shape. I am now trying to calculate the are of the shape ...
2
votes
2answers
263 views

Why is QGIS Field calculator button greyed out?

I'm using QGIS to attempt to calculate the area enclosed by a set of points that I have capture used a GPS device. I have imported the coordinates from a CSV but when trying to open the field ...
1
vote
1answer
190 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 ...
3
votes
1answer
226 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
2answers
312 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
95 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 ...
0
votes
2answers
230 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 ...
1
vote
1answer
60 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. ...
3
votes
2answers
538 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.
4
votes
1answer
254 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
589 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 ...
5
votes
3answers
318 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 ...
6
votes
1answer
357 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
737 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 ...
6
votes
1answer
530 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 ...
5
votes
2answers
1k 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 ...
1
vote
1answer
100 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 ...
8
votes
3answers
649 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
542 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 ...
6
votes
1answer
2k 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" ...
3
votes
1answer
737 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 ...
3
votes
1answer
251 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 ...
5
votes
2answers
4k 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?
2
votes
1answer
1k views

Convert area from square meters to degrees globally

I have a global raster file with 3600x1800 pixels. I don't have any information about the projection used. The raster contains one band with a quantity with the unit "per square meter". How can I ...
1
vote
1answer
274 views

How can the scale be projected correctly in Quantum GIS when it is imported from google earth (KML) files?

While importing KML files from google Earth to Quantum GIS, the scale is not being projected properly and the area of a particular selected feature is not being calculated in the attribute table by ...
2
votes
1answer
448 views

Why does intersect not calculate polygon areas?

this is strange: I intersected 2 shape-files and the resulting shape does not contain the Shape_Area and Shape_Length of the intersected polygons. Instead the field Shape_Area contains the ...
4
votes
2answers
287 views

Total newbie. Creating map from aerial photo of golf course in QGIS

I have a aerial photo in tif with a tfw file of the golf course that I work at. I would like to create vector data of different features on the course such as greens fairways tees, etc. to calculate ...