Count points in polygon - Revision history

⚠️Madi: /* Geometry based solution */

2015-04-19T08:07:36Z

Geometry based solution

← Older revision		Revision as of 08:07, 19 April 2015
Line 55:		Line 55:
	[[Category:FAQ]]		[[Category:FAQ]]
	[[Category:Vector]]		[[Category:Vector]]
			[[Category:HowTo]]

⚠️Madi: /* Geometry based solution */

2015-04-19T08:02:12Z

Geometry based solution

← Older revision		Revision as of 08:02, 19 April 2015
Line 48:		Line 48:
	== Geometry based solution ==		== Geometry based solution ==

	* {{cmd\|v.vect.stats}} counts the number of points falling into each polygon and optionally calculates statistics from numeric point attributes for each polygon. v.vect.stats is a C module and available from GRASS 6.4.3 and later.		* {{cmd\|v.vect.stats}} counts the number of points falling into each polygon and optionally calculates statistics from numeric point attributes for each polygon. v.vect.stats is a C module and available from GRASS 6.4.3 and later. {{cmd\|v.vect.stats}} creates the columns for updating the data automatically, alternatively it is also possible to update existing column, provided that the type is integer.

			{{cmd\|v.vect.stats}} points=mypoints areas=mypolygons count_column=pointcnt


	[[Category:FAQ]]		[[Category:FAQ]]
	[[Category:Vector]]		[[Category:Vector]]

Neteler: +TOC

2014-06-17T08:57:03Z

+TOC

← Older revision		Revision as of 08:57, 17 June 2014
Line 1:		Line 1:
			__TOC__

	'''Q:''' How can I count the number of points which fall into polygons?		'''Q:''' How can I count the number of points which fall into polygons?

	'''A:''' Carry over an attribute from the polygons to the points, then count the number of equal attributes by SQL grouping.		'''A:''' there are two options:

			== Attribute based solution ==

			Carry over an attribute from the polygons to the points, then count the number of equal attributes by SQL grouping.

	Example: How many archaeological sites does each parcel owner have?		Example: How many archaeological sites does each parcel owner have?
Line 40:		Line 46:
	BY owner" \| db.select		BY owner" \| db.select

	== ~~Alternative~~ solution ==		== Geometry based solution ==

	* {{cmd\|v.vect.stats}} counts the number of points falling into each polygon and optionally calculates statistics from numeric point attributes for each polygon. v.vect.stats is a C module and available from GRASS 6.4.3 and later.		* {{cmd\|v.vect.stats}} counts the number of points falling into each polygon and optionally calculates statistics from numeric point attributes for each polygon. v.vect.stats is a C module and available from GRASS 6.4.3 and later.

Neteler: v.vect.stats in core GRASS

2012-12-31T12:54:32Z

v.vect.stats in core GRASS

← Older revision		Revision as of 12:54, 31 December 2012
Line 42:		Line 42:
	== Alternative solution ==		== Alternative solution ==

	* {{~~AddonCmd~~\|v.vect.stats}} counts the number of points falling into each polygon and optionally calculates statistics from numeric point attributes for each polygon. v.vect.stats is a C module and ~~works with~~ GRASS 6.4 ~~and higher (see enclosed patches for 6~~.5 and ~~7.0)~~.		* {{cmd\|v.vect.stats}} counts the number of points falling into each polygon and optionally calculates statistics from numeric point attributes for each polygon. v.vect.stats is a C module and available from GRASS 6.4.3 and later.

	[[Category:FAQ]]		[[Category:FAQ]]
	[[Category:Vector]]		[[Category:Vector]]

Neteler: /* Alternative solution */

2012-10-03T12:05:14Z

Alternative solution

← Older revision		Revision as of 12:05, 3 October 2012
Line 45:		Line 45:

	[[Category:FAQ]]		[[Category:FAQ]]
			[[Category:Vector]]

Neteler: +v.vect.stats

2011-08-12T07:10:58Z

+v.vect.stats

← Older revision		Revision as of 07:10, 12 August 2011
Line 39:		Line 39:
	echo "SELECT ,count(owner) FROM myarchsites WHERE ""cat in (select from MyCats)"" GROUP \		echo "SELECT ,count(owner) FROM myarchsites WHERE ""cat in (select from MyCats)"" GROUP \
	BY owner" \| db.select		BY owner" \| db.select

			== Alternative solution ==

			* {{AddonCmd\|v.vect.stats}} counts the number of points falling into each polygon and optionally calculates statistics from numeric point attributes for each polygon. v.vect.stats is a C module and works with GRASS 6.4 and higher (see enclosed patches for 6.5 and 7.0).

	[[Category:FAQ]]		[[Category:FAQ]]

⚠️Craigleat at 15:22, 31 March 2009

2009-03-31T15:22:42Z

← Older revision		Revision as of 15:22, 31 March 2009
Line 1:		Line 1:
	'''Q:''' How can I count the number of points which fall into polygons?		'''Q:''' How can I count the number of points which fall into polygons?

	'''A:''' Carry over an attribute from the polygons to the points, then count the number of equal attributes by SQL grouping:		'''A:''' Carry over an attribute from the polygons to the points, then count the number of equal attributes by SQL grouping.

	Example: How many archaeological sites does each parcel owner have?		Example: How many archaeological sites does each parcel owner have?

Line 30:		Line 31:
	v.db.select myfields		v.db.select myfields

	The resulting ~~polygon~~ table contains the number of points falling into each polygon.		The resulting table contains the number of points falling into each polygon.

			Caveat:
			The above approach counts attributes and not features. This means that if there is more than one category linking a feature to rows in the table you will count more categories than there are features. It is also possible that many features link to one category and in this case you will under count the number of features. The first scenario may arise by using v.edit to remove duplicates e.g. Point A and point B are snapped to produce point C (features A and B are deleted) and feature C inherits the attributes of A and B. Two categories now link to feature C. To use the above approach to count points with extra categories it is necessary to create a new table and populate it with categories such that there is a 1:1 correspondence between features and categories. The new table (MyCats) can then be used as a filter e.g.

			# test run
			echo "SELECT ,count(owner) FROM myarchsites WHERE ""cat in (select from MyCats)"" GROUP \
			BY owner" \| db.select

	[[Category:FAQ]]		[[Category:FAQ]]

⚠️Craigleat at 06:33, 27 January 2009

2009-01-27T06:33:05Z

← Older revision		Revision as of 06:33, 27 January 2009
Line 25:		Line 25:
	g.copy vect=fields,myfields		g.copy vect=fields,myfields
	v.db.addcol myfields col="numpoints integer"		v.db.addcol myfields col="numpoints integer"
	v.db.update myfields column=numpoints value="(SELECT count(owner) FROM myarchsites WHERE myarchsites.owner=myfields.label GROUP BY owner);"		v.db.update myfields column=numpoints value="(SELECT count(owner) FROM myarchsites WHERE \
			myarchsites.owner=myfields.label GROUP BY owner);"
	# verification:		# verification:
	v.db.select myfields		v.db.select myfields

	The resulting polygon table contains the number of points falling into each polygon.		The resulting polygon table contains the number of points falling into each polygon.

			[[Category:FAQ]]

Neteler: New FAQ

2009-01-26T21:10:10Z

New FAQ

New page

'''Q:''' How can I count the number of points which fall into polygons?

'''A:''' Carry over an attribute from the polygons to the points, then count the number of equal attributes by SQL grouping:
Example: How many archaeological sites does each parcel owner have?

# Spearfish area
# (Note: DBF driver unsupported, please use SQLite, MySQL or PostgreSQL)
g.copy vect=archsites,myarchsites
v.db.addcol myarchsites col="owner varchar(25)"

We now transfer the owner names to the archaeological sites (points):

v.what.vect myarchsites qvect=fields column=owner qcolumn=label
# verification:
v.db.select myarchsites

d.mon x0
d.vect -c fields
d.vect myarchsites icon=basic/diamond size=10

# test run
echo "SELECT *,count(owner) FROM myarchsites GROUP BY owner" | db.select

# upload to polygons map
g.copy vect=fields,myfields
v.db.addcol myfields col="numpoints integer"
v.db.update myfields column=numpoints value="(SELECT count(owner) FROM myarchsites WHERE myarchsites.owner=myfields.label GROUP BY owner);"
# verification:
v.db.select myfields

The resulting polygon table contains the number of points falling into each polygon.