en-us http://www.bostongis.com Features the latest GIS tutorials on postgis, mapserver and other GIS technologies Boston GIS (mailto:articles@paragoncorporation.com) <h1>What Is PostGIS?</h1> <p>PostGIS is an open source, freely available, and fairly OGC compliant spatial database extender for the PostgreSQL Database Management System. In a nutshell it adds spatial functions such as distance, area, union, in http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_tut01 2010-02-23 Paragon Corporation (mailto:support@paragoncorporation.com) <p>We gave a presentation on writing PostGIS spatial queries at <a href="http://en.oreilly.com/oscon2009/public/schedule/detail/7859" target="_blank">OSCon 2009 last week</a>. Slides will be available on the site, but you can download them <a href="/down http://www.bostongis.com/PrinterFriendly.aspx?content_name=oscon2009_postgis_spatial_tricks 2009-07-30 Paragon Corporation (mailto:support@paragoncorporation.com) <p>We gave a lecture at PGCon 2009. Below are the links and the generated data set. Some of the examples use features in PostgreSQL 8.4 and PostGIS 1.4, but most should be applicable to earlier versions. The data generation part does use PostgreSQL 8.4 http://www.bostongis.com/PrinterFriendly.aspx?content_name=pgcon2009_postgis_spatial 2009-05-23 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>What is SpatiaLite?</h1> <p>SpatiaLite is an SQLite database engine with Spatial functions added. You can think of it as a spatial extender for SQLite database engine which is similar in concept to what PostGIS does for the PostgreSQL Object-Rel http://www.bostongis.com/PrinterFriendly.aspx?content_name=spatialite_tut01 2009-03-28 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>No Aggregates, what's a girl to do?</h1> <p>Those who read our PostGIS series may be wondering why the examples we chose were not the same as what we did for PostGIS. Sadly SQL Server 2008 does not have any built-in spatial aggregates such as those http://www.bostongis.com/PrinterFriendly.aspx?content_name=sql2008_tut03 2008-11-11 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>Bringing in Towns As Geography (Geodetic) -- Continued</h1> <p>In the first part we covered bringing in Mass Towns data as Planar geometry, but were stuck because we need to transform the data to a degree based projection (in particular one listed in http://www.bostongis.com/PrinterFriendly.aspx?content_name=sql2008_tut02 2008-11-05 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>What Is SQL Server 2008?</h1> <p>Microsoft SQL Server 2008 is the first version of SQL Server to have built-in functionality for doing geographic spatial queries.</p> <p>This tutorial is similar to our <a href="/PrinterFriendly.aspx?co http://www.bostongis.com/PrinterFriendly.aspx?content_name=sql2008_tut01 2008-10-31 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>What is ST_Dump, Dump </h1> <P> ST_Dump is a function that takes a geometry and returns a set of Postgis <b>geometry_dump</b> structure. Geometry_dump is composed of 2 properties. <i>geom</i> and <i>path</i>. The geom is a geometry and path is a mu http://www.bostongis.com/postgis_dump.snippet 2008-06-23 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>What is GDAL and RGDAL?</h1> <P>GDAL stands for Geospatial Data Abstraction Library and is a popular open source GIS library originally developed and maintained by <a href="home.gdal.org/warmerda/" target=_blank>Frank Warmerdam</a> with contributions http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgresql_plr_tut03 2008-03-14 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>ST_Translate, Translate</h1> <p>The ST_Translate function takes any geometry (linestring, multiline etc) returns a new geometry that is the original geometry moved by a vector defined by X,Y,Z. Note the units of measurement are always in the units http://www.bostongis.com/postgis_translate.snippet 2007-10-16 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>ST_Intersects, Intersects</h1> <P> ST_Intersects is a function that takes two geometries and returns true if any part of those geometries is shared between the 2. In PostGIS versions before 1.3 you would use the following syntax to utilize indexes < http://www.bostongis.com/postgis_intersection_intersects.snippet 2007-09-21 Paragon Corporation (mailto:support@paragoncorporation.com) <P>ST_Summary(geometry) gives you a brief summary of a geometry telling you how many simple geometries, rings and type of geometry it is. </P> <CODE> select ST_Summary(the_geom) from neighborhoods; </CODE> <b>Output of the above ran from psql looks like http://www.bostongis.com/postgis_st_summary.snippet 2007-08-24 Paragon Corporation (mailto:support@paragoncorporation.com) <H1>A generic solution to PostGIS nearest neighbor</H1> <P>After some heavy brainstorming, I have come up with a faster and more generic solution to calculating nearest neighbors than my previous solutions. For the gory details on how I arrived at this s http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_nearest_neighbor_generic 2007-08-01 Paragon Corporation (mailto:support@paragoncorporation.com) <P>A common problem encountered in GIS is the Nearest Neighbor problem. In a nutshell the problem is to find the x number of nearest neighbors given a geometry and n geometries of data. </P> <P>The nearest neighbor crops up in other disciplines as wel http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgis_nearest_neighbor 2007-07-21 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>PL/R and PostGIS</h1> <p>In this tutorial we will explore using PostGIS and PL/R together. Some examples we will quickly run thru. <br> </p><ul><li>Median Function in conjunction with PostGIS</li> <li>Voronoi Diagrams</li> </ul> <p>If you mi http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgresql_plr_tut02 2007-06-20 Paragon Corporation (mailto:support@paragoncorporation.com) <p>R is both a language as well as an environment for doing statistical analysis. R is available as Free Software under the GPL. For those familiar with environments such as S, MatLab, and SAS - R serves the same purpose. It has powerful constructs for ma http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgresql_plr_tut01 2007-06-17 Paragon Corporation (mailto:support@paragoncorporation.com) <H1>Creating Point Geometries with ST_MakePoint</H1> <P>There are numerous ways of creating point geometries in PostGIS. We have covered these ways in other snippets. Check out the fulling links for other examples. </P> <UL> <LI><a href="postgis_geomfr http://www.bostongis.com/postgis_makepoint.snippet 2007-06-02 Paragon Corporation (mailto:support@paragoncorporation.com) <P>In this tutorial we will just show some example snippets of using OpenLayers that we have found most useful. We will be assuming Open Layers 2.4 and above. </P> <h1>Initializing Layers Off</h1> In our previous example, you will notice that all the l http://www.bostongis.com/PrinterFriendly.aspx?content_name=openlayers_tut_02 2007-05-30 Paragon Corporation (mailto:support@paragoncorporation.com) <H1>Loading Well-Known-Text (WKT) using ST_PointFromText, ST_LineFromText, ST_MPointFromText, MLineFromText, MPolyFromText, PolyFromText</H1> <b>Syntax:</b> ST_PointFromText(<i><a href="http://en.wikipedia.org/wiki/Well_Known_Text" target=_blank>wkt repre http://www.bostongis.com/postgis_pointfromtext_linefromtext_etc.snippet 2007-05-25 Paragon Corporation (mailto:support@paragoncorporation.com) <h1>Extent Expand Buffer Distance ST_DWithin</h1> <P>In this quick exercise, we will explore the following PostGIS OGC functions: Extent, Expand, Buffer, Distance <br /> </P> <h2>Extent</h2> <P>Extent is an aggregate function - meaning that it is used jus http://www.bostongis.com/postgis_extent_expand_buffer_distance.snippet 2007-04-29 Paragon Corporation (mailto:support@paragoncorporation.com)