Baltimore Buildings Import

Work In Progress

This import is currently being worked on.

About

This page intends to detail the process of importing building outlines provided by the City of Baltimore. Addresses will be assigned using a parcel map.

Building outlines source: https://data.baltimorecity.gov/Geographic/Building-Footprint-Shape/deus-s85f
Parcel map source: https://data.baltimorecity.gov/Geographic/Parcels-Shape/jk3c-vrfy

Method

Outline Simplification

Import Data into Database

• Create Postgres database named "buildings".

-- Add PostGIS extensions
create extension postgis;

• Import buildings Shapefile and add "cleanGeometry" function.

shp2pgsql -s 2248 building.shp buildings | psql -d buildings
psql -d buildings < cleanGeometry.sql

Simplify Outlines while Preserving Topology

Based on http://trac.osgeo.org/postgis/wiki/UsersWikiSimplifyPreserveTopology.

-- Extract multipolygons into polygons
create table poly as (
    select gid, (st_dump(geom)).*
    from buildings
);
create index poly_geom_gist on poly using GIST(geom);

-- Extract rings out of polygons
create table rings as (
    select st_exteriorRing((st_dumpRings(geom)).geom) as geom
    from poly
);
create index rings_geom_gist on rings using GIST(geom);

-- Simplify rings (takes a long time)
create table simplerings as (
    select st_simplifyPreserveTopology(st_linemerge(st_union(geom)), 0.000001) as geom
    from rings
);
create index simplerings_geom_gist on simplerings using GIST(geom);

-- Extract lines from simplified rings
create table simplelines as (
    select (st_dump(geom)).geom as geom
    from simplerings
);
create index simplelines_geom_gist on simplelines using GIST(geom);

-- Rebuild polygons from lines (takes a long time)
create table simplepolys as (
    select (st_dump(st_polygonize(distinct geom))).geom as geom
    from simplelines
);
alter table simplepolys add column gid serial primary key;
create index simplepolys_geom_gist on simplepolys using gist(geom);

-- Clean building geometry
create table simple_buildings as (SELECT cleangeometry(geom) as geom FROM simplepolys);

-- Remove interior courtyards (takes a long time)
create table bunion as (select (ST_Dump(ST_Union(ST_MakeValid(geom)))).* as geom from poly);
delete from simple_buildings where not exists (
    select * from bunion
    where st_intersects(bunion.geom, simple_buildings.geom)
    and st_area(st_intersection(bunion.geom, simple_buildings.geom))/st_area(simple_buildings.geom) > 0.5
);

Validate Simplified Data

Manually review and fix validation errors and warnings.

Address Assignment

To do.

Licensing

The data download pages says the data is "Public Domain," but the website Terms of Use page has conflicting licensing statements. Attempts to clarify licensing terms with the City are in progress.