Lessons Learned from Experiments with PostGIS

Eleanor Tutteleanor@rhcda.com

St. Louis

What is PostGIS?

Eleanor Tutt | Lessons Learned from Experiments with PostGISProvidence NNIP Meeting | September 2012

• Free and Open Source• Adds support for geographic objects to

PostgreSQL database (which is also open source)

Why Experiment ??

Eleanor Tutt | Lessons Learned from Experiments with PostGISProvidence NNIP Meeting | September 2012

• Growing quantity of data• Increasingly complex analysis needs• Tired of seeing this in ESRI help files:

Continued Concerns

Eleanor Tutt | Lessons Learned from Experiments with PostGISProvidence NNIP Meeting | September 2012

• Other priorities besides shuffling data• Fear of reliance on a lesser-known

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The experiment so far…

Eleanor Tutt | Lessons Learned from Experiments with PostGISProvidence NNIP Meeting | September 2012

Frustrating - Projections

Eleanor Tutt | Lessons Learned from Experiments with PostGISProvidence NNIP Meeting | September 2012

• Need SRID to properly import data (and if you forget, you don’t get a warning)

Frustrating - Projections

Eleanor Tutt | Lessons Learned from Experiments with PostGISProvidence NNIP Meeting | September 2012

• SRID has to be in “spatial_ref_sys” table (and not all codes are there by default)

Where’s my SRID???

Frustrating – Projections

Eleanor Tutt | Lessons Learned from Experiments with PostGISProvidence NNIP Meeting | September 2012

• No “on the fly” projection – must be constantly aware of SRID and use ST_Transform any time SRIDs don’t match

Exciting – Increased Speed

Eleanor Tutt | Lessons Learned from Experiments with PostGISProvidence NNIP Meeting | September 2012

• ArcGIS takes up to 45 seconds to get past the splash screen (let alone adding data)…

• …when half the time, my queries are simple and don’t require a “pretty map” (“Which bus routes are within a half mile of a site?”)

Exciting – New Analysis Capabilities

Eleanor Tutt | Lessons Learned from Experiments with PostGISProvidence NNIP Meeting | September 2012

• Drive time polygons/routings

• Converting polygons to lines/splitting lines into line segments

• So much more…

Exciting – ESRI + PostGIS!

Eleanor Tutt | Lessons Learned from Experiments with PostGISProvidence NNIP Meeting | September 2012

ArcMap Query Layers + PostGIS

Eleanor Tutt | Lessons Learned from Experiments with PostGISProvidence NNIP Meeting | September 2012

Side Benefits – Better Understanding of ArcGIS

Eleanor Tutt | Lessons Learned from Experiments with PostGISProvidence NNIP Meeting | September 2012

• Learning a different language helps you think in different ways

• What is intuitive in one system may be possible, but easy to miss, in the other

Side Benefits – Opportunity for “Data Audit”

Eleanor Tutt | Lessons Learned from Experiments with PostGISProvidence NNIP Meeting | September 2012

“Export_Output_2.shp”“test_data.shp”“RHCDA20110418.shp”

Conclusions???

Eleanor Tutt | Lessons Learned from Experiments with PostGISProvidence NNIP Meeting | September 2012

• Dealing with projections is incredibly frustrating – especially with data from two states

• Learning curve is steep, but climb-able

• We aren’t ready to leave ArcGIS, yet