Avoid polygons overlap (#636)

Author: alex-cit

src/.vitepress/sidebar/en.js

@@ -55,6 +55,7 @@ export default {
         { text: 'How to Set Photo Names Format', link: '/gis/photo-names/' },
         { text: 'How to Enable Digitising', link: '/gis/enable_digitising/' },
         { text: 'How to Set Up Snapping for Mergin Maps Mobile App', link: '/gis/snapping/' },
+        { text: 'How to Avoid Polygons Overlap', link: '/gis/avoid-overlap/' },
         { text: 'Custom Projections', link: '/gis/proj/' },
         { text: 'Supported Formats', link: '/gis/supported_formats/' }
       ]

src/field/mobile-features/index.md

@@ -147,6 +147,13 @@ If snapping is enabled, the crosshairs will turn purple and snap to vertices (le
 
 3. Fill in the attributes and **Save** :heavy_check_mark: the changes
 
+## Avoid polygons overlap
+In QGIS, you can set the option to avoid overlapping for polygons. This setting is stored in the <MainPlatformName /> project and used when editing features both in QGIS and the <MobileAppNameShort />.
+
+See [How to Avoid Polygons Overlap](../../gis/avoid-overlap/) for more details.
+
+![Mergin Maps mobile app avoid polygon overlap](../../gis/avoid-overlap/mobile-avoid-polygon-overlap.jpg "Mergin Maps mobile app avoid polygon overlap")
+
 ## Deleting features
 
 1. Tap on a feature on the map or find it through [**Layers**](../../field/layers/)

src/gis/avoid-overlap/index.md

@@ -0,0 +1,44 @@
+# How to Avoid Polygons Overlap
+
+For polygon layers, <QGISHelp ver="latest" link="user_manual/working_with_vector/editing_geometry_attributes.html#overlapping-control" text="QGIS" /> offers options to control the overlapping. In the **Snapping toolbar**, you can set if you want to allow or avoid overlaps when digitising new features. 
+
+<MobileAppName /> follows this setting: if you create a polygon that overlaps existing geometries in the layer, the polygon will be cropped and snapped to the existing features. 
+
+You can apply this option for the [active layer](#avoid-overlap-on-active-layer) or use [advanced configuration](#follow-advanced-configuration-to-control-overlapping) to define which layers should be avoided when digitising new polygons.
+
+## Avoid overlap on active layer
+To use the *Avoid overlap* option in your <MainPlatformName /> project:
+1. Open your project in QGIS
+2. Make sure that the **Snapping toolbar** is visible in the toolbar panel.
+   
+   If not, click on the toolbar panel and activate the **Snapping** toolbar.
+
+   ![Activated Snapping toolbar in QGIS](./qgis-activate-snapping-toolbar.jpg "Activated Snapping toolbar in QGIS")
+
+3. In the **Snapping toolbar**, select the *Avoid overlap on Active Layer* option or [*Follow Advanced Configuration*](#follow-advanced-configuration-to-control-overlapping)
+
+   ![QGIS Snapping toolbar - Avoid overlap on Active Layer](./qgis-avoid-overlap.jpg "QGIS Snapping toolbar - Avoid overlap on Active Layer")
+
+4. Save and synchronise your project.
+
+Now this option will be used when digitising new polygons both in QGIS and the <MobileAppNameShort />:
+
+![Mergin Maps mobile app avoid polygon overlap](./mobile-avoid-polygon-overlap.jpg "Mergin Maps mobile app avoid polygon overlap")
+
+## Follow advanced configuration to control overlapping
+
+It is also possible to set advanced configuration to control overlapping of multiple polygon layers. This is useful if you want to digitise polygons that will be cropped and snapped to existing features from *multiple* layers.
+
+1. Open your project in QGIS
+
+2. In the **Snapping toolbar** use *Open Snapping Options...* to open the **Project Snapping Settings**
+   ![QGIS Snapping toolbar - Open Snapping Options](./qgis-snapping-options.jpg "QGIS Snapping toolbar - Open Snapping Options")
+
+3. In **Project Snapping Settings**, switch to *Advanced Configuration* and choose *Follow Advanced Configuration* for overlap control.
+ 
+   Now select relevant layers in the *Layer* column and tick the *Avoid Overlap* option for those layers that should use this overlap control option.
+   
+   ![QGIS Snapping toolbar - Advanced configuration](./qgis-snapping-options-advanced-config.jpg "QGIS Snapping toolbar - Advanced configuration")
+   
+4. Save and synchronise your project
+