Creating Convex Hulls with SQL to QGIS: Part 1

In order to create clusters based on foursquare categories, we first made a table in PostgreSQL called upperlevelcat and assigned a gid for each of the nine categories.

Foursquare Categories:

upperlevel cat table

To link these categories to venues, we did a double join : fscategory table, fsvenue, and fsvenue_fscategory tables.

fscategory table

fscategory2

fsvenue table

fsvenue table

fsvenue_fscategory

fsvenue_fscategory

SQL statement for double join:

SELECT v.herenow, v.checkinct, v.userct, join1.upperlevelcat, join1.name as catname, v.name as venuename,v.lat,v.lon,v.geom

FROM (SELECT * from fsvenue_fscategory

LEFT JOIN fscategory as fsc ON fsc.fsid=fsvenue_fscategory.cid) AS join1

LEFT JOIN fsvenue as v ON  v.fsid=join1.vid

Result

result

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