Map from point-data to region data in Python

Question

I have a dataset that lists entities per district - where district is a named shape that exists on a map. I have a different dataset that contains entities of the same type, only instead of being positioned categorically (i.e. by district name) they are positioned using lat-long coordinates.

So, given a shapefile (in either ESRI or GML3), how can I transform a list of lat-long coordinates into a matching list of named districts?

I am looking for the most generic algorithm possible, but if there are tools/modules out there that perform this function natively, that would be good to know too.

Answer 1

One of the easiest ways of doing this would be to import the data into PostGIS and use an update function similar to the following

UPDATE coord_list SET coord_districts = (SELECT district_name FROM polygon_districts WHERE ST_Within(coord_list.geom,polygon_districts.geom)

So you would have to add in a field called coord_districts (or whatever you want to call it really) to your point dataset and this query will update this field based on which district it is found in.

Answer 2

Here is an alternative to the answer above using QGIS (I'm using Nodebo version):

1) Save your list of lat and long coordinates in a .csv file; put aside.

2) Load your district layer (I assume it is a polygon layer).

3) Load your .csv file asa point layer

• Layer > Add Layer > Add Delimited Text Layer
• Browse for your .csv file
• Choose "Point Coordinates" radio button in the Geometry Definition
• Select your lat and long column (be careful: lat is Y, long is X)
• more info http://www.qgistutorials.com/en/docs/importing_spreadsheets_csv.html

4) Perform "Join Attributes by Location" in QGIS or spatial join (in ArcMap)

• In QGIS nodebo search "join attributes by location" in the processing toolbar.

• Sekect your csv (points) layer as target layer.

• Select your district layer as join layer.

• In the geometric predicate group, choose "within" radio button.

• Run the tools

5) Save the resulting layer in a .csv file

• Right click the layer.
• Choose "Save as.."
• Select .csv