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I have two vector layers, one is a GeoJSON (can be downloaded from https://pastes.io/vtlw5surdx) which contains countries with points and their coordinates in WGS84 CRS and one layer is shapefile created by Vector > Research Tools > Create Grid then the coordinates for grid extent are -180,180,-90,90 [EPSG:4326] and Horizontal and Vertical spacing are set to 18 degrees.

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Then, I created New Print Layout with Atlas

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and everything looks fine with this setting:

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But then after I chose Atlas > Export Atlas as images and I opened 200 output generated tiff files on QGIS again, it has some invalid rasterized labels like below. How can I avoid that?

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1 Answer 1

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The reason for the "false" labels result from the uncommon usage of Atlas-Exports as "Raster-Catalog-Re-Import" in QGis, not from the tile-creation itself.

Simplified:

Exporting an atlas means dynamically "scroll" through the features of a vector-layer, zoom to each feature-extent, create a map-image, decorate it with other layout-elements, thus creating a graphic-file or PDF for each feature. The vector-layer-label-placement is done individually for each exported tile. According to common layer-label-settings most labels are dynamically positioned or even omitted for better readability, especially in the margins. Re-Importing these georeferenced tiles in QGis as kind of "Raster-Catalog" shows the actually identical labels at different positions or with partial overlaps from other tiles.

Solution:

  1. The above used atlas-page-layout is rectangular, but the map-element inside the page is quadratic and the created grid-layer has quadratic geometries. Exporting this layout creates raster-images with blank areas at both sides, which will overlap if used as reimported raster-catalog. Making the layout quadratic and the map-element fill the whole area will create images without blank areas and without the overlap-problem.
  2. Additionally to avoid missing or double labels you can define label-settings with constant placement "Offset from Point" and Placement Engine Settings "Allow truncated labels on edges of map"
  3. Additionally to get exported symbols and labels with the same size as in the original map you can set all size-properties (line-width, symbol-size, font-size, buffer-width etc.) to be in map-units instead of pixel or point.

Problems remaining are points or labels near a tile-border and very long labels , here you must fiddle with label-settings and/or manual feature/label-placement.

Original Map in QGis: Original Map in QGis

Same map atlas-exported and re-imported as raster-images: Same map atlas-exported and re-imported as raster-images

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