{"id":4490,"date":"2024-05-16T01:19:53","date_gmt":"2024-05-16T01:19:53","guid":{"rendered":"https:\/\/blogs.lincoln.ac.nz\/gis\/?p=4490"},"modified":"2024-05-16T01:19:54","modified_gmt":"2024-05-16T01:19:54","slug":"bivariate-curious","status":"publish","type":"post","link":"https:\/\/blogs.lincoln.ac.nz\/gis\/bivariate-curious\/","title":{"rendered":"Bi(variate) Curious"},"content":{"rendered":"\n

Using Bivariate Symbology on a map of housing prices<\/em><\/p>\n\n\n\n

We’ve been looking at different mapping strategies lately and this time we’ll look at an uncommon one, uncommon enough that people are likely to be curious about how it works. I will admit that I, too, have been curious, having never really used it before. The method? Bivariate Colors<\/a>. In their own words, ESRI says this method “shows the quantitative relationship between two variables in a feature layer,” whatever that means. The basic idea is that you’re trying to map two different quantities at one time using solid colours to show the differences. <\/p>\n\n\n\n

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In theory, this allows you to show how a feature varies across two attributes. It’s two mints in one!<\/a> And a potential doubling of displayed information – or possibly doubling the confusion… This came to mind when working with postgrad Reina who was wanting to map study site locations in terms of two variables: whether a farm was a monoculture or a diverse operation and whether the study was done at the farm or catchment scale. Initially we thought she would need two separate maps, but perhaps Bivariate Colors would work here? Let’s find out.<\/p>\n\n\n\n

We started with a layer of 185 study sites within Aotearoa spread across the motu: <\/p>\n\n\n\n

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In the table I’ve got an attribute that tells me at what scale the study was done (Farm or Catchment) and another about the operation type (Monoculture or Diverse):<\/p>\n\n\n\n

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To get started with Bivariate Colors, we can choose that as the Primary symbology:<\/p>\n\n\n\n

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This opens the settings window:<\/p>\n\n\n\n

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Field1 and Field2 are where I can set the attributes to be mapped, but one of the first things I notice is that it doesn’t honour text fields, meaning I can only use numerical types for this. So I added two new attributes, ScaleNum and DiverseNum and populated them so that,<\/p>\n\n\n\n