field-calculatorqgis
I have a shapefile that consists of a list of archaeological sites with the x and y coordinates.
I have an Natural Earth shapefile for the countries of world.
I was wondering how I go about creating a new field for the country of each archaeological site using the field calculator?
I am relatively new to QGIS and not that familiar with the field calculator.
If you're committed to using the Field Calculator tool your best bet may be a very short python script within the "Pre-Logic Script Code":
def listShpName(yourShp):
desc=arcpy.Describe(yourShp)
return desc.Name
...and then your expression will be
listShpName("LayerInArcMapToC")
Where LayerInArcMapToC is the name of your layer in ArcMap
I've attached a screen capture to illustrate this. Of course, you'll have to do this on a shapefile-by-shapefile basis if you want to use field calculator. Here's a link to the ESRI documentation on describing data like I've illustrated above: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//002z00000018000000
An additional link to some simple field calculator operations: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//005s0000002m000000
Short Answer: Directly You can't.
Long Answer: Join the layer that contains the inputfield, to the layer that contains the field your want to calculate. After this, you can definetly use the input field in your Python Code.
Best Answer
Two options.
1.) Perform an intersect of the points with the countries. Use
Vector > Geoprocessing Tools > Intersect...For the intersect tool, make the input your arch sites (points) and your intersect layer as the countries (polygons).
That will produce a point file with the attributes from the countries attached to each point.
2.) If you know that the points do not overlap more than one polygon, then it's also possible to use the field calculator to do that quickly.
Install the refFunctions plugin for QGIS.
You can calculate a new field quickly in QGIS 2.8.1 by highlighting your arch points layer in the layer list, then pressing the Field Calculator button. Or do it from the attribute table.
Then use the new
geomintersectsfunction in theReferencelist:geomintersects('target layer','target field')Where
target layeris the name of the countries layer, andtarget fieldis the field of the named countries to attach to the points.There are some other functions like
geomwithinthat may work in this case too.