OpenStreetMap- Field Calculator to Merge/Flatten Layer Attributes?

Question

I'm not sure exactly what I am asking, probably lending to my struggle to figure it out via google.

I have a large polygon layer from OpenStreetMap data (openstreetmap.org). My problem is I need to reduce/generalize the fields/attributes in that layer largely due to inconsistencies in classifications from different people adding to it.

For example, I have the value field "leisure" with polygons labeled "garden", "golf course", etc. I have another value field with polygons/attributes "grass", "meadow", etc.

Is there a way to create a new value field or separate polygon layer with all these polygons labeled as "greenspace"?

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I am still struggling to figure out how to use the field calculator to do what I am looking for. I think my hang up is that I am trying to combine polygons of different "attributes" within different field types (attaching image to original post for clarification). Is there a way to combine polygons of several values (not fields) from different fields into one field?

Answer 1

Unfortunately, this is going to require a lot of manual work on your part to sort through the different values in the field and categorise them according to your requirements.

The first step would be to determine which classifications you want. For example, you mentioned greenspace as one category. I'm assuming you'll have other classifications as well: commercial, residential, industrial, etc.

Once you have those determined, you'll need to get a list of all of the existing values in your field and determine which of your categories they fall into. You can get a full list by using the Summary Statistics tool.

Then, you can add a new field. One way to do this is with the Add Field tool. Then, select all of the records you want to change (garden, golf course, grass, meadow, etc) and then use the field calculator to update to the value you want - "Greenspace". Repeat the process for other classifications you require.

If you're feeling ambitious, and want to use python, you can create an expression in the field calculator on your new field to populate based on different values in the other field. There are plenty of examples on this site for doing that (like this one, or this one), so I won't go into detail here.