GIS Tool in Drupal PNW Drupal Summit - Seattle October 20th, 2012 Mack Hardy & Tom

History of Maps with Drupal Tools

Location Module, proximity and filter

Storage and Import

Storage - GeoField Where do we store data in drupal? A common field format for geodata WKT Lat Lon Bounding

Spatial Import How do we import data from external sources? Shapefiles KML files Uses GeoPHP and ogr2ogr Spatial module -> Saves as WKT -> Geofield

ogr2ogr Wrapper module for the GDAL ogr2ogr library - Spatial module calls ogr2ogr - Converts data from source formats to WKT

Query

Sync_PostGIS Module Allows drupal to query PostGIS as a spatial query service, much in the way SOLR is used for search Syncs data from Drupal entities with geofields to PostGIS Provides query methods for testing intersection, within, buffer conditions

Sync_PostGIS Module

What does sync_postgis tell us? Intersections with other data points Within a buffer of 5km

Testing for Intersection function geoquery_intersects($item1, $item2) { $params = array($item1, $item2); foreach ($params as &$param) { if (is_scalar($param)) { $param = array('entity_type' => 'node', 'eid' => $param); } if ($connection = sync_postgis_get_postgis_connection()) { $geo_query = new syncPgQuery($connection); return $geo_query->booleanRelQuery('intersects', $params[0], $params[1])->execute(); }

Testing for Buffer Distance function geoquery_dwithin($item1, $item2, $distance = 0, $srid = 4326) { $params = array($item1, $item2); foreach ($params as &$param) { if (is_scalar($param)) { $param = array('entity_type' => 'node', 'eid' => $param); } if ($connection = sync_postgis_get_postgis_connection()) { $geo_query = new syncPgQuery($connection, $srid); return $geo_query->booleanRelQuery('dwithin', $params[0], $params[1], $distance)->execute(); }

Displaying the results With the results from the PostGIS backend, we can show the user useful information In this case they know that - target is in the protected area - target intersects 2 traplines - target is within a 5 km buffer of 4 other nodes of interest

Scaling

Beyond Vector Based Maps We want to show huge datasets, the vector model requires "painting" the data onto the map, which is computationally expensive Pre-rendering the dataset onto a tile, means the client can load the data quickly, and tiles are easy to cache Obvious downside of caching, is that it doesn't work well with frequently changing data Tilemill has been great for creating base tiles, but regenerating the entire tileset when the data changes is hard and time consuming

Comparing Vector vs MB Tiles Vector MB of transfer - Client side render Tiles kB of transfer - Server side render

Tilestache Python application for serving tiles tilestache takes inputs of : --- mbtiles which are pre-generated --- mapnik configuration (to generate tiles on the fly) --- vector (geojson, arcjson) --- combinations of these inputs as composite We are generating using mapnik with PostGIS as a datasource - provides a caching layer for serving tiles

Composite maps from PostGIS Data base map satellite images tilestache provides the data layers from PostGIS via mapnik leaflet map definition points to layers in the layer switcher Image credit

WAX interactivity parcel data with tiles in JSON on mouseover and on click behaviours need to pre-cache WAX styling

WAX interactivity

Demo

WAX interactivity How UTF8 grid works

Random Tools

Leaflet Draw

Leaflet Paste

Search API Next we want to be able to return data items from SOLR to a map Search on non-geographic facets - just like a view Search on geographic facets - facet controls pull data from PostGIS, or use SOLRs spatial extensions

Discussion