Database Reference
In-Depth Information
209 nodes, 304 edges, 97 faces, 60
topogeoms in 1 layers+
Layer 1, type Polygonal (3), 60
topogeoms +
Deploy:
chp03.hu_topo_polygons.the_geom_topo
+
10. The problem is easily identifiable by analyzing the
hu_topo.face
table or
usingaDesktopGIS.Ifyousortthepolygonsfromthistablebyarea,using
the
ST_Area
function, you will notice after the details of the first polygon,
which has one null area (used by the topology screenshot in the next step)
and 20 large areas (each representing one administrative area), that there
are 77 very small polygons generated by topological anomalies (polygon
overlaps and holes):
postgis_cookbook=# SELECT row_number()
OVER (ORDER BY ST_Area(mbr) DESC) as
rownum, ST_Area(mbr)/100000 AS area FROM
hu_topo.face ORDER BY area DESC;
rownum | area
------------+--------------------
1 |
2 | 366365.476705923
3 | 313236.739489454
...
21 | 20662.4948917497
22 | 8.12994437170007
23 | 6.72174611815608
...
97 | 0.0164102556404216
98 | 0.014788623905157
(98 rows)
11. Youcaneventuallylookatthebuilttopologyelements(nodes,edges,faces,
andtopogeoms)usingaDesktopGIS.Thefollowingscreenshotshowshow
they look in QGIS:
