Hot answers tagged area
14
Google Maps Mania blog points to example of Swiss Administrative Boundaries Map:
The code from Vasile is on github.
10
I generally use the character ² or U+00B2. So it is km², without requiring any special formatting.
If you have a MS Windows keyboard, type the sequence: Alt+0178
Other platforms have different ways of typing this character. You can also copy/paste the Unicode character. More info: http://www.fileformat.info/info/unicode/char/b2/index.htm
9
Here's a link to some code that'll yield the area of a simple polygon (originally from the World Wind Forum): http://forum.worldwindcentral.com/showthread.php?t=20724. This solves the problem on a sphere, roughly based on the relationship:
S = area of polygon;
theta is the sum of interior angles in radians;
n is the number of vertices;
r is the radius of ...
9
Open field calculator, select the new column and type the following expression
For area: $area
For perimeter: $perimeter
Make sure your layer is in a projected coordinate system (not lat/long ) and in correct units. ( i.e. if your layer's projection has 'meters' as units, your area will be square meters )
8
Accuracy of calculated results depends on a number of discrete processes, which can all compound inaccuracy in the final dataset.
The importance of Metadata in this situation, is it can be used to explain error and even identify steps error is introduced.
The most important thing is to understand that ground truthing your results, if performed correctly ...
7
Try this formula (assuming your source is WGS1984, if not then you'll need to adjust the ellipsoid used by the second line):
area = rad(x2 - x1) * (2 + sin(rad(y1)) + sin(rad(y2))) + rad(x3 - x2) * (2 + sin(rad(y2)) + sin(rad(y3))) + rad(x4 - x3) * (2 + sin(rad(y3)) + sin(rad(y4))) + rad(x5 - x4) * (2 + sin(rad(y4)) + sin(rad(y5)))
area = abs(area * ...
7
PostGIS 1.5 introduced a new GEOGRAPHY type. The GEOGRAPHY type allows for unprojected coordinates on a spheroid to be stored in a PostGIS table, and some analysis functions to be performed upon them.
ST_Area queries can be performed upon GEOGRAPHY type polygons in order to calculate their area in square meters.
The following query outputs the area of ...
7
This is a problem that everyone solves with a slight difference. IMHO, Yahoo did a great job with WOEIDs.
As far as what is the most efficient way, it seems the answer is too subjective and dependent on your application.
7
It is a consequence of a theorem of Archimedes (c. 287-212 BCE) that for a spherical model of the earth, the area of a cell spanning longitudes l0 to l1 (l1 > l0) and latitudes f0 to f1 (f1 > f0) equals
(sin(f1) - sin(f0)) * (l1 - l0) * R^2
where
l0 and l1 are expressed in radians (not degrees or whatever).
l1 - l0 is calculated modulo 2*pi (e.g., -179 ...
7
For the Project coordinate reference system, you have to choose a projected CRS, which uses real metres as units. Openlayers Plugin uses Google mercator, which is only corresponding to real meters at the aequator. The further north you come, the more distorted the length units are (look at Greenland in Openstreetmap, it is not so big in reality).
By ...
6
Almost all global rasters twice as long as high, and especially those with numbers of rows and columns being nice multiples of 180, use ("unprojected") geographic coordinates. Therefore this one almost surely uses square cells of 0.1 degree. Please confirm this in the grid's metadata if possible.
The conversion from square degree to square meter depends on ...
6
You have a closing paren in the wrong place towards the end of your query. I tried this and got a NaN return,
SELECT ST_AREA(ST_Transform(ST_GeomFromText('POLYGON((871325.790874952 6105405.3261047,871418.748307692 6105359.72944624,871346.22022442 6105215.141258,871254.85408906 6105261.72007212,871325.790874952 6105405.3261047))',4326),31467)) As sqm;
...
5
Kirk
If you are doing this within Arcmap and you have an open table, have you ruled out using the Calculate Geometry option after right-clicking on the field. If your dataframe is already set in the projection that you want you should be able to use its coordinate system without the prior projection issue.
5
Here is the really easy way. Add a field to your existing feature class. Right click on the field title and choose "Calculate Geometry". You'll then have the option to pick your desired coordinate system and units of measure.
One note: This calculation is static, so you will need to recalculate anytime you make changes.
5
The latest PostGIS has a "Geography" data type which does calculations on Lat/Lon WGS84 spatial reference system data, and returns the distance or area results in meters/sq. meters based on the WGS84 ellipsoid. So you could bring your country data into PostGIS in WGS84 Lat/Lon, using Geography instead of Geometry and then create the buffers, and do the area ...
5
As MappaGnosis indicated, you could write a little script for this. Here's one called polygonbuffer which takes three arguments: The output file name, the radius of your buffer, and the number of corners of the polygons.
Open a Python console in QGIS, paste the script and press enter to define the function, then call using something like ...
5
if you´re looking for something like this(labels denote area in sqkm):
You can just intersect the Fishnet with the Polygon Layer.
5
There are three different ways to find and store polygon area into a feature class with arcpy: 1) field calculator, 2) "classic" arcpy cursors, and 3) arcpy.da cursors. Some of this is borrowed from my previous answer about using SearchCursor.
1. Field calculator
When using field calculator, there are three different expression types that use different ...
5
I would recommend clipping the raster to the shapefile, then in the resulting raster you can look at the number of cells present for each of your classes. The area can be calculated by multiplying the number of cells by the area covered each pixel (cell size squared).
It's a different approach than the equally valid solution offered above but from a ...
4
Here's the source for the simplified calculation that we make in OpenLayers. This method comes from "Some Algorithms for Polygons on a Sphere" (Robert. G. Chamberlain and William H. Duquette, NASA JPL Publication 07-03). The code linked to above is for determining the area of a linear ring (with geographic coordinates). Areas for Polygons and ...
4
You'll need to convert your geographic coordinates into a projection that has a coordinate system that allows you to use Cartesian math to calculate area.
I believe UTM is the accepted standard projection, as it is very simple to select a zone based on your latitude and longitude, and also the distortion is minimal, even across zones. So, if you have a ...
4
You can temporally re-project the data on the fly in arcmap and use
CTRL+SHIFT+G to open the Calculate Geometry dialog box
and calculate the area with the current projection (meter/feet)
after the field is populated you can go back to WGS84 but the area will remain (unless you recalculate the area again)
4
A digital image of a map where the only information you have is "1:50000 scale" doesn't have a true scale. You need some indication of distance to use a dimensionless scale, and all the image has is pixels. On paper, those pixels are explicitly related to a physical size.
There are some customary standards for relating paper resolution to pixel scale, but ...
4
This is a quick and dirty way to do it: Add some data (such as roads, buildings or water) to ArcMap from the region you know the map is in. Add the .jpg. Add the Georeferencing toolbar and georeference the jpg. Click a control point on the .jpg first and then match it to the same location in the spatial data, like a street intersection or the corner of a lot ...
4
Not trying to be terse, but given that you are using shapefiles it may be reasonale to assume you might have access to ArcGIS. If so, the directions here:
http://soa.utexas.edu/crp/gis/arcgis_tips/area_calculation.html
are quite clear.
then simply select the polygon and look at your attribute table.
Answer GetSpatial's question and there are plenty of ...
4
You first need to import the CSV file with v.in.ascii to create a vector points map. Add a new column "Country" of varchar(25) with v.db.addcol. Then simply populate the new column with v.what.vect (see also example in that manual page).
4
In R, the gIntersection() tool from the rgeos package should intersect and match the data, but doesn't seem to be working (gives only the shapes, not the dataframes (see @ari-b-friedman's question).
QGIS will work for you if you use the Vector|Geoprocessing|Intersect tool, giving you a set of all the points with the overlapping country data merged; this is ...
4
You're looking for the Dissolve tool - if all of your polygons are in the same featureclass/layer just run it and then use the Field Calculator to determine the area.
If your polygons are in different featureclasses, run the Merge or Append tool first.
4
Region Group on your original classified raster will identify 'patches' and assign them each a unique number in the VALUE field. Note: an item called LINK is added to the attribute table of the output raster, which indicates the original value for each cell from the input raster.
You can use the Zonal Geometry As Table tool again to get the area in map ...
3
You could also try using the MaxMind GeoLite City dataset. This dataset is a point layer that contains both the AreaCode and MetroCode (Example: AreaCode - MetroCode - XXXX). If you have a metrocode, you might be able to get closer than just with area code by finding the nearest City point that shares both the area code and metrocode of the phone number ...
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