{"id":3876,"date":"2023-03-01T10:50:51","date_gmt":"2023-02-28T21:50:51","guid":{"rendered":"http:\/\/blogs.lincoln.ac.nz\/gis\/?p=3876"},"modified":"2023-03-30T04:35:26","modified_gmt":"2023-03-30T04:35:26","slug":"spatial-joins-made-easy","status":"publish","type":"post","link":"https:\/\/blogs.lincoln.ac.nz\/gis\/spatial-joins-made-easy\/","title":{"rendered":"Spatial Joins Made Easy"},"content":{"rendered":"

We cover a quick and easy way to do temporary spatial joins<\/em><\/p>\n

When we opened up the mail bag here at GIS Central recently, out popped a request from a colleague: “Do we have a mapping table of LAWA monitoring site names to the regional council site names?”  Perhaps I should decode this a bit before we get to a solution.<\/p>\n

LAWA is Land, Air, Water Aoteroa<\/a>, a consortium of regional councils, DOC, MFE and several others<\/a> (Ed.: Egads!  Government working together…?!?<\/em>) that aims to provide public access to  monitoring data on our natural resources.<\/p>\n

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When you want to find out which beaches have the best water quality for swimming<\/a>, this is probably where you’ll end up:<\/p>\n

\"\"<\/a><\/p>\n

My colleague had a layer of these water quality monitoring sites but the attributes didn’t include which region each site was in.  Could GIS help?  Absolutely.  And in getting to a solution we discovered a nice quick way to do some temporary spatial joins.<\/p>\n

So let’s start with the data.  The monitoring sites were in the form of a .gpkg file.  The is a geopackage<\/a>, a format I’ve not come across much but is basically an open-source data container for sharing spatial data.  It’s a nice compact way to share data as email attachments, for example.  Pro can read these like many of the data formats available<\/a>, so it was easily added to a map:<\/p>\n

\"\"<\/a><\/p>\n

You can see that the attribute table is pretty simple – the main information available is the “lawaid”, a unique identifier for each of the 1,013 sites.  What’s missing is information on what region each site is in.  Let’s address that by adding a layer of the regional council boundaries (J:\\Data\\Administrative_Boundaries\\regional_council_2018_clipped.shp):<\/p>\n

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Also a relatively simple layer, the most useful thing being the REGC2018_1 attribute which has the name of each region.  At this point, these are two separate layers on the map and I need to come up with some way to bring all the attributes together in to one layer, ideally so that I have a single layer with regional council names attached to each site.  I can’t do a table join<\/a> as there’s no common attribute between the two layers so I need to use their locations do to the join.  This suggests that I could use a spatial join<\/a> tool, such as Intersect<\/a>, Identity <\/a>or Union<\/a>.  These tools create a new layer that combines the input layers based on their locations.<\/p>\n

In this latest version of Pro (3.0.3 as of this writing) I discovered a handy new addition that could save me a few steps.  In the Contents pane, clicking on the layer name gets you a context menu – we’re looking for Joins and Relates and what’s under there:<\/p>\n

\"\"<\/a><\/p>\n

Those of you used to doing Table Joins will be familiar with this menu – very handy.  The new addition here is “Add Spatial Join”, so let’s check that out.<\/p>\n

\"\"<\/a><\/p>\n

The Target Features are the LAWA sites while the Join Features come from the regional council layer.  Intersect is a good option for the match but be aware that there are lots of others.  When I click OK, the attribute values from the the regional council layer that intersects with the LAWA point layer are added in the table:<\/p>\n

\"\"<\/a><\/p>\n

Nifty, now with this layer we know the region that each site is in.<\/p>\n

One important note is that this join is temporary.  If I add this layer to another map, or send it to someone else, the regional council data won’t be a part of it.  To make it permanent I would need to make a new copy of the data (right-click the layer name > Data > Export Features).<\/p>\n

My next step was to export this table as a CSV file that my colleague could use.  Job done.<\/p>\n

Most of the time, GIS only gives me trouble and heartache (I exaggerate…slightly) so it was nice that I could help out a colleague and do it quite easily.  And once again, we get to see the value of spatial joins.  This won’t be the last time.<\/p>\n

C<\/p>\n","protected":false},"excerpt":{"rendered":"

We cover a quick and easy way to do temporary spatial joins When we opened up the mail bag here at GIS Central recently, out popped a request from a colleague: “Do we have a mapping table of LAWA monitoring site names to the regional council site names?”  Perhaps I should decode this a bit […]<\/p>\n","protected":false},"author":3,"featured_media":3961,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-3876","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/posts\/3876","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/comments?post=3876"}],"version-history":[{"count":2,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/posts\/3876\/revisions"}],"predecessor-version":[{"id":3971,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/posts\/3876\/revisions\/3971"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/media\/3961"}],"wp:attachment":[{"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/media?parent=3876"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/categories?post=3876"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/tags?post=3876"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}