Canvas UIs, like those used in mapping applications and design tools, provide users with an interactive experience similar to manipulating a physical canvas. The article discusses the development of a geospatial canvas for Felt's drawing tools, focusing on core concepts such as coordinate systems, gestures, and viewport transformations. The canvas UI relies on a combination of world-space (geographic coordinates) and screen-space (pixel coordinates) systems to allow users to pan and zoom effectively, using gestures that maintain the geographic point under the cursor during zooming. Felt's system employs map tiles, exponential zoom levels, and techniques like Mercator projection to manage geographic data efficiently. To optimize performance, particularly when rendering complex shapes, the system uses GPU-accelerated SVG transformations and transient canvas transforms, which reduce the computational load during interactions. Regular reprojections are performed to maintain accuracy across a wide zoom range, dynamically simplifying geometries based on zoom level to avoid unnecessary computation. This sophisticated setup ensures that Felt's canvas UI remains responsive and efficient as users create increasingly intricate maps.