# 10. Geometry Exercises¶

Here’s a reminder of all the functions we have seen so far. They should be useful for the exercises!

• sum(expression) aggregate to return a sum for a set of records

• count(expression) aggregate to return the size of a set of records

• ST_GeometryType(geometry) returns the type of the geometry

• ST_NDims(geometry) returns the number of dimensions of the geometry

• ST_SRID(geometry) returns the spatial reference identifier number of the geometry

• ST_X(point) returns the X ordinate

• ST_Y(point) returns the Y ordinate

• ST_Length(linestring) returns the length of the linestring

• ST_StartPoint(geometry) returns the first coordinate as a point

• ST_EndPoint(geometry) returns the last coordinate as a point

• ST_NPoints(geometry) returns the number of coordinates in the linestring

• ST_Area(geometry) returns the area of the polygons

• ST_NRings(geometry) returns the number of rings (usually 1, more if there are holes)

• ST_ExteriorRing(polygon) returns the outer ring as a linestring

• ST_InteriorRingN(polygon, integer) returns a specified interior ring as a linestring

• ST_Perimeter(geometry) returns the length of all the rings

• ST_NumGeometries(multi/geomcollection) returns the number of parts in the collection

• ST_GeometryN(geometry, integer) returns the specified part of the collection

• ST_GeomFromText(text) returns geometry

• ST_AsText(geometry) returns WKT text

• ST_AsEWKT(geometry) returns EWKT text

• ST_GeomFromWKB(bytea) returns geometry

• ST_AsBinary(geometry) returns WKB bytea

• ST_AsEWKB(geometry) returns EWKB bytea

• ST_GeomFromGML(text) returns geometry

• ST_AsGML(geometry) returns GML text

• ST_GeomFromKML(text) returns geometry

• ST_AsKML(geometry) returns KML text

• ST_AsGeoJSON(geometry) returns JSON text

• ST_AsSVG(geometry) returns SVG text

Also remember the tables we have available:

• nyc_census_blocks

• blkid, popn_total, boroname, geom

• nyc_streets

• name, type, geom

• nyc_subway_stations

• name, geom

• nyc_neighborhoods

• name, boroname, geom

## 10.1. Exercises¶

• What is the area of the ‘West Village’ neighborhood?

SELECT ST_Area(geom)
FROM nyc_neighborhoods
WHERE name = 'West Village';

1044614.5296486

Note

The area is given in square meters. To get an area in hectares, divide by 10000. To get an area in acres, divide by 4047.

• What is the geometry type of ‘Pelham St’? The length?

SELECT
ST_GeometryType(geom),
ST_Length(geom)
FROM nyc_streets
WHERE name = 'Pelham St';

ST_MultiLineString
50.323

• What is the GeoJSON representation of the ‘Broad St’ subway station?

SELECT
ST_AsGeoJSON(geom)
FROM nyc_subway_stations
WHERE name = 'Broad St';

{"type":"Point",
"crs":{"type":"name","properties":{"name":"EPSG:26918"}},
"coordinates":[583571.905921312,4506714.341192182]}

• What is the total length of streets (in kilometers) in New York City? (Hint: The units of measurement of the spatial data are meters, there are 1000 meters in a kilometer.)

SELECT Sum(ST_Length(geom)) / 1000
FROM nyc_streets;

10418.9047172

• What is the area of Manhattan in acres? (Hint: both nyc_census_blocks and nyc_neighborhoods have a boroname in them.)

SELECT Sum(ST_Area(geom)) / 4047
FROM nyc_neighborhoods
WHERE boroname = 'Manhattan';

13965.3201224118

or…

SELECT Sum(ST_Area(geom)) / 4047
FROM nyc_census_blocks
WHERE boroname = 'Manhattan';

14601.3987215548

• What is the most westerly subway station?

SELECT ST_X(geom), name
FROM nyc_subway_stations
ORDER BY ST_X(geom)
LIMIT 1;

Tottenville

• How long is ‘Columbus Cir’ (aka Columbus Circle)?

SELECT ST_Length(geom)
FROM nyc_streets
WHERE name = 'Columbus Cir';

308.34199

• What is the length of streets in New York City, summarized by type?

SELECT type, Sum(ST_Length(geom)) AS length
FROM nyc_streets
GROUP BY type
ORDER BY length DESC;

type                       |      length
--------------------------------------------------+------------------
residential                                      | 8629870.33786606
motorway                                         | 403622.478126363
tertiary                                         | 360394.879051303
motorway_link                                    | 294261.419479668
secondary                                        | 276264.303897926
unclassified                                     | 166936.371604458
primary                                          | 135034.233017947
footway                                          | 71798.4878378096
service                                          |  28337.635038596
trunk                                            | 20353.5819826076
cycleway                                         | 8863.75144825929
pedestrian                                       | 4867.05032825026
construction                                     | 4803.08162103562
residential; motorway_link                       | 3661.57506293745
trunk_link                                       | 3202.18981240201
primary_link                                     | 2492.57457083536
living_street                                    | 1894.63905457332
primary; residential; motorway_link; residential | 1367.76576941335
undefined                                        |  380.53861910346
steps                                            | 282.745221342127
motorway_link; residential                       |  215.07778911517

Note

The ORDER BY length DESC clause sorts the result by length in descending order. The result is that most prevalent types are first in the list.