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Discover how to fix inaccurate marker placements on `flutter_map` when zooming out. Follow our steps for accurate positioning and effective use of OpenStreetMap tiles.
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This video is based on the question https://stackoverflow.com/q/75542158/ asked by the user 'Salar Azad' ( https://stackoverflow.com/u/6243913/ ) and on the answer https://stackoverflow.com/a/75611635/ provided by the user 'Salar Azad' ( https://stackoverflow.com/u/6243913/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Enhance Your flutter_map Experience: Accurate Marker Placement Made Easy

When working with maps in Flutter, particularly with flutter_map and OpenStreetMap tiles, developers may encounter a common issue: inaccurate marker placements when zooming out. This can lead to markers appearing floating above their intended locations, causing confusion for users. In this guide, we'll explore this issue and provide a straightforward solution that will help you achieve accurate marker positioning on your map.

Understanding the Problem

You may have encountered a situation where, after implementing markers for specific coordinates on a map, they do not align correctly when zoomed out. Instead of remaining fixed relative to their geographical coordinates, the markers seem to float, making your app's map hard to use and understand.

Example Scenario

Consider the following scenario where you're using the flutter_map package to display an OpenStreetMap tile:

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While the markers are placed at specific LatLng points, zooming out on the map causes them to not align properly with the expected coordinates. This highlights the importance of ensuring that markers stay true to their designated positions.

The Solution: Using a Center Widget

After troubleshooting the issue, it was discovered that wrapping the Image.asset widget within a Center widget resolves the placement inaccuracies of the markers. Here’s how to implement it:

Step-by-step Instructions

Wrap the Asset Image: Modify the builder property of the Marker to wrap your Image.asset with a Center widget. This adjustment ensures that the marker remains centered on its designated point when zoomed at various levels.

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Example Modified Marker Code:

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Test the Map: After making this change, run your app again and examine the behavior of your markers at different zoom levels. They should now stay accurately aligned with their respective coordinates.

Additional Note on Anchor Position

While it is worth mentioning that changing the anchorPos property to AnchorPos.align(AnchorAlign.center) is also an option, it may not yield significant changes since the default position is already centered. Thus, the Center widget approach is often the most reliable fix.

Conclusion

Inaccurate marker placements in flutter_map can be a frustrating issue, but with the simple solution of wrapping your asset images in a Center widget, you'll greatly enhance your users' map experience. By ensuring your markers remain accurately aligned at various zoom levels, you can build a more user-friendly interface for your application. Happy coding!