tags: PostGIS

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PostGIS

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GIS (3), PostgreSQL (1), database (1), bailey (1), OSM (1), programming (1), population (1), planet (1), TIGER (1), up-to-date (1), map (1), census (1), density (1), PostgreQL (1), beer (1),

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GIS, PostGIS

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Coastal's Blog: How to get an up-to-date OSM in PostGIS

Andrew Bailey

Rather than doing a quarterly manual job of downloading a 14Gb+ file, decompressing it (250Gb+) and inserting it into a database it will be a lot easier to download daily (50Mb) OSM change files (.osc) and apply the changes to the existing database.

The instructions below is a modified version of Martin van Exel's tutorial here - https://docs.google.com/document/pub?id=1paaYsOakgJEYP380R70s4SGYq8ME3ASl-mweVi1DlQ4

url: http://coastalrocket.blogspot.com/2012/09/how-to-get-up-to-date-osm-in-postgis.html

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Exploding Polygons Into Random Points by Density with PostGIS | Geo Perspectives

Visualizing geo-data by density is a common need but often leaves us with yet another chloropleth map.  Sometimes there is a need to make the data more visually interesting or to capture multiple characteristics of that density in one layer.  This can be the case with race and ethnicity data where visualizing race and density simultaneously can be very powerful.  The University of Virginia’s Racial Dot Map is an excellent example of this.

url: http://jmapping-maplabs.rhcloud.com/exploding-polygons-into-random-points-by-density-with-postgis/

type: article, format: blog

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Paul Ramsey

tags: GIS, PostGIS
the clever elephant Paul Ramsey Victoria, British Columbia, Canada

url: http://blog.cleverelephant.ca/

type: person, format: blog

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Reprojecting / snapping point-geometries onto a given line-geometry using PostGIS

tags: PostGIS, GIS
a line and several points

Imagine you have a line — a street for example — and point measurements taken while being on that street. Due to certain circumstances — e.g. GPS-coorrdinates are slightly inaccurate –, the coordinates of your measurements are not exactly on the street.

url: http://selectoid.wordpress.com/2009/02/13/reprojecting-snapping-point-geometries-onto-a-given-line-geometry-using-postgis/

type: article, format: blog

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Selectoid's Weblog

A detail showing four stars we just created Hi, this is the blog of selectoid

url: http://selectoid.wordpress.com/

type: person, format: blog

Programming

After a long day at work of arduous programming, i come home to do what? Yes more programming. But wait there's a difference. At home, i can sip my beer while waiting for code to compile.

At work today i was able to take the Tiger dataset and draw a map. Tiger comes with only line data, ie. only one dimensional. However for each chain of points there are attributes referring to adjacent polygons. Using tigerpoly.py in the GDAL project i was able to construct the 2 dimensional polygons.

All that data was inserted into a PostgreSQL database with PostGIS installed. PostGIS and GDAL needed a couple patches. Then i wrote a Java program to grab the data using JDBC and drew it using AWT. Sure Java2D is better, but i'm not sure i need it. After all i'm just drawing lines and polygons. Sheesh.

I'm guessing all map data comes from the same source. The Census Bureau. Therefore, even Google (eventually) gets their data from Tiger. How is it different? Well (1) the roads have width proportional to the number of lanes, (2) all the corners are rounded, and (3) their roads are labelled. Those are the major differences in appearance. As for differences in feel, don't get me started.

And on a side note, it's been so long that i almost forgot my password to my own website. Back to dinner (Otter Creek Alpine Ale).