QGIS Atlas – How to Filter Layers in QGIS Atlas

atlasfilterfmeqgis

In processing several spatial data sets (tbl_data_01, tbl_data_02, tbl_data_03, etc) using FME I establish a spatial table called "tbl_metadata" with information about each of the data set. This table holds the metadata (if available) and the layer name for each of the spatial data sets. A spatial object, a rectangular envelope, is also established.

I would like to use tbl_metadata to produce an atlas (a dataset fact sheet) in QGIS 3 for each of the spatial data sets. The atlas should present a map sheet showing each spatialdata set as well as a table with the available metadata. The spatial data sets have already been read in to the project.

I have read several presentations doing something similar. One is to use the coverage layer to highlight the current atlas feature using a conditional (@atlas_featureid = $id) or even selecting certain objects in a separate layer based on a feature name. An option could also be to define presets. But this latter method requires manual adjustments.

Is there a method to use the atlas table (here tbl_metadata) to filter/add the associated spatial data sets to respective maps in the atlas?

Best Answer

You can use the tbl_metadata file as coverage layer in Atlas. Then use rule-based symbology with @layer_name = @atlas_pagename.

I assume that your data looks like this (the attribute table is tbl_metadata table):

Set the tbl_metadata as Coverage layer and select the field with dataset name as Page name. If you want to hide the coverage layer geometry, check Hidden coverage layer.

In the map item Item Properties check Controlled by Atlas. This ensure that extent of features (rectangular envelope) will control the zoom of map item.

Now you have to change symbology of each layer to Rule-based and add rule: @layer_name = @atlas_pagename, the layer than will be symbolised only if the layer name is equal to current atlas page name.

Add attribute table item with . Select tbl_metadata as a layer and set the filter to "dataset" = @atlas_pagename, this filter only the rows where value of dataset is equal to atlas page name.

Run the atlas preview

Note: QGIS can read also .csv files as layer without geometry, which can be also used as coverage layer. In that case you can skip the step 2. The zoom will not be controlled by geometry and will be fixed (since it is table without geometry).

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QGIS Atlas – How to Use with Multiple Layers or Files per Coverage

Since QGIS 2.12, with the introduction of data-defined properties on the "lock layers for map" option, in the map item properties, you can do what you seek. You just need to create the right coverage layer, with the information of the extents, but also of the layers to "print".

Create the layer presets

You can "save" the current state (visible or not visible) of your layers as presets. Just create the desired combination and press the eye icon on the layers panel, and choose "add preset".

Basically, you will have to create a preset for each contour, with that layer visible (paired with other layers if you like). This will be your "set of layers".

Give your preset memorable names, or else just opt for some kind of a sequence.

Creating the coverage layer.

Now you will have to create a polygon layer with all the possible combinations between the extents polygons, and all the presets. That means you will end up with some redundancy. You will have to replicate each extent polygon for each preset. Something like this:

polygon 1, preset a polygon 1, preset b ... polygon 50, preset a polygon 50, preset b

You can do this manually with copy paste, or else create some kind of script, but I would say your best and easier way would be using Spatialite or Postgis database. Just import you polygons extents there, and create a new non-spatial table with all presets names. Then, create a view that returns all the combinations.

SELECT f.*, g.preset_name
FROM polygons_extent as f, presets as g

Making it work

Add the new layer or view to QGIS, use it as coverage layer in atlas settings, and use the preset_name attribute in data-defined properties on the "lock layers for map" option.

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The tables are not being read because the user permissions (I believe for Admin) were not turned on inside the MS-Access DB. I turned them on for all the tables and QGIS loaded the tables (albeit somewhat slowly).

Best Answer

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QGIS Atlas – How to Use with Multiple Layers or Files per Coverage

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