# Tagged Questions

Area is a quantity that expresses the extent of a two-dimensional surface or shape, or planar lamina, in the plane.

2answers
6k views

### Is it possible to gray out a Google Maps map except for some area?

What i am looking for is a way to emphasize a certain area on a Google Maps map by graying out the rest of the world. I heard about some solution of using 2 polygons of which 1 is visible and the ...
5answers
9k views

### How can I measure area from geographic coordinates?

If I have polygons in geographic coordinates (WGS84), how do I measure the total area each takes on the surface of the earth, taking into account the curvature of the earth?
7answers
11k views

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

I am 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. ...
1answer
10k 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 ...
1answer
291 views

### Circle area calculation in QGIS is inaccurate

I created a circle with a radius of 3 km, calculated the area using field calculator and got a different result from real area. The QGIS result is 28273078.8 while manually calculated area is ...
2answers
591 views

### More accurate way to calculate area of rasters

In my daily work, I am constantly asked to calculate areas of global raster datasets in geographic projection at 30 arc second resolution. These datasets are normally the result of a Combine operation ...
2answers
1k views

### Projections appropriate for global analysis that preserve area and that preserve distance (but not necessarily in the same projection)

I am looking for a projection (or a set of projections) that decently preserve distances so that I can buffer every country in the world and have a similar level of minimal distortion for each. I ...
2answers
20k 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?
3answers
5k 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 6105215....
1answer
7k views

### How to measure areas of features in OpenLayers plugin background maps correctly?

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" toolbar, and i have tried fTools in ...
2answers
4k 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 ...
3answers
2k views

### Calculating area of vegetation in 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.
2answers
1k 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 ...
2answers
633 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, it'...
1answer
471 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 antemeridian,...
4answers
8k views

### How to recalc WGS84 Shape_Area field to square miles in ArcGIS 10

What are the units of the Shape_Area field in a wgs84 feature class? Is it decimal degree squared? I would like to convert that to something more meaningful like square miles without reprojecting the ...
2answers
442 views

### Deleting polygons smaller than certain dimension using ArcGIS for Desktop?

I've made a model in modelbuilder in Arcmap 10.3, what it basically does is creating polygons over open areas such as farm-lands, grass-lands, marshes etc that has a low slope. My challenge is that I ...
3answers
838 views

### How can I obtain the same area values provided by the Census for TIGER boundaries using PostGIS functions?

In PostGIS, how can I compute the area of Census Boundaries and obtain the same results as are provided by the Census? For example, most Census Boundaries include attributes for Land Area and Water ...
2answers
783 views

### QGIS area calculation differs when on the fly CRS transformation enabled

When I open QGIS, add the layer, and calculate the areas of the shapefile via field calculator I get a different area than when I open QGIS and check "Enable on the fly CRS transformation" and ...
1answer
749 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 ...
1answer
6k views

### Calculating area of an EPSG:4326 Polygon [duplicate]

Possible Duplicate: What is the most accurate coordinate system for calculating areas of polygons? In our Postgres/Postgis database we store polygons in a column defined as lonlat/EPSG:4326, ...
1answer
100 views

### Dividing the world space to geographic sub-space

I am trying to divide the world space to geographic sub-space from "general" to "specific" locations and without using latitude and longitude information. That is, I am trying to think about the world ...
2answers
592 views

### Wrong \$area from field calculator (QGIS)

The area of the polygons in a layer, calculated by the field calculator with "\$area" is wrong (much too big) for some polygons. If I draw the concerned polygon again, the area is calculated correctly. ...
2answers
1k 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 ...
2answers
3k views

### Openlayers geometry: how to convert area from degrees to square kilometres?

I get a multypolygon from my web service and want to calculate the area of that polygon. I was trying to use this piece of code: var poly = new OpenLayers.Geometry.MultiPolygon(poligon); var area = ...
1answer
1k 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 ...
0answers
722 views

### How to split polygons without ArcView? [closed]

I'm trying to split polygons into equal areas. While fishnet sort of works; the areas I'm trying to split don't touch; they're national parks. Fishnet spans the whole area, not just the polygons in ...
2answers
3k 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 ...
2answers
5k views

### Converting Longitude and Latitude Coordinates to Square Miles?

I have a set of Long and Lat co-ordinates making up a five point polygon which I have converted in excel using the following formula: =((X1*Y2)-(X2*Y1)+(X2*Y3)-(X3*Y2)+(X3*Y4)-(X4*Y3)+(X4*Y5)-(X5*Y4)+...
1answer
334 views

### Geometry Calculation

Wanted to ask about accuracy of areas calculated by GIS compared to actual ones on ground. Because I have data of my country without areas for the districts within Uganda. Are the areas obtained using ...
2answers
2k views

### Shapefiles for U.S. Area Codes (NANP)

I have a bunch of telephone numbers (just the area codes), and I'd like to geolocate them and make a map, but I haven't had too much luck googling for shapefiles for Area Codes. Surely these are in ...
2answers
361 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 ...
1answer
510 views

### Tabulate Area ArcGIS

I am trying to work out the relationship between the 'processing cell size' and the result from Tabulate Areas. If one uses the same as the raster cell size, and this is the same for both rasters, the ...
3answers
756 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 ...
1answer
637 views

### Cannot compute area of shapefile in field calculator of QGIS?

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 ...
3answers
1k views

### Remove Holes Existing Within a Single Polygon for a specific area in Qgis

I have a shapefile that consists of a single polygon. I have gaps within the polygon that needs to be eliminated, but only the ones that are less than 200m2. I tried different ways but none of them ...
4answers
658 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 ...
1answer
295 views

### Equal area projections with different area results in ArcGIS for Desktop?

Using ArcGIS, I have to calculate areas of huge polygons all over the Pacific Oceans betwwen 20N and 30S. I have been trying different Equal-areas projections (Cylindrical and sinusoidal for example) ...
2answers
354 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 ...
1answer
3k views

### Calculating geometry area in ArcGIS for Desktop using ArcPy?

I have a polygon shapefile and I want to write a Python script to add a field named "area" and calculate its geometry areas. The script is like this: arcpy.AddField_management("...
2answers
778 views

### How to compute area in acres in QGIS?

I am new to QGIS. I am creating a shapefile that will have several polygons. I need to have a column in the attribute table that will show the acres of each polygon. I have successfully done this but ...
2answers
1k 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 ...
1answer
580 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. ...
1answer
2k views

### How to display Radius after Resizing a Feature in Openlayers

@captDragon has helped me with calling the coordinates of a polygon after I have resized or dragged the feature. Ineed the radius now, i have done a radius alert on my other map,Which works correctly, ...
1answer
121 views

### Routing ensuring all areas are touched

I'm making a web application with leaflet and OSM. It's all going well, but now I need a little help. I'm searching for a good routing engine, that's capable of creating the most probably taken route ...
1answer
111 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 ...
2answers
2k views

### How to find the area of raster values within polygon zones?

I'm using ArcGIS 9.3 and I just can't seem to get this right - I've tried tabulate areas, zonal stats, converting to polygons, etc. I'm missing something somewhere. I have a USGS impervious surface ...
1answer
144 views

### Comparing floor and roof areas using QGIS?

I am pretty new in this GIS topic and I would really appreciate if someone can help me with this problem. I am doing a research for university that shall show the available roof area for ...
1answer
451 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 ...
0answers
35 views

### Projecting polygon when calculating its area? [duplicate]

I have a broad range of polygons (in vector format and in SpatialPolygonsDataFrame class), some going east-west, others going south-north, while even others span polar regions or very large ranges as ...