Loading Basemap Without Center or Setting View in Map Initialization

How to Enhance User Experience with Leaflet Maps When the Center Coordinates Load Slowly

In the world of Web GIS, providing a smooth and user-friendly experience is always a goal. Recently, I encountered an issue where I needed to create a map using Leaflet, but the center coordinates, which were crucial for the initial view, were being fetched from a slow-loading layer. This delay resulted in users initially being greeted by a blank map container, which is far from ideal. In this blog post, I’ll share how I tackled this issue to improve the user experience by ensuring that a base map is always visible while waiting for the center coordinates to load.

The Problem

While working on a mapping project, I used the Leaflet JavaScript library to display various geographic data layers. My setup involved initializing a map with multiple layers and a specific center point that was dynamically fetched from another data source. The asynchronous nature of this data fetch meant that if the data layer took too long to load, the user would initially see a blank area instead of a map.

Here’s the original map initialization code:

view.map = L.map('map_' + mapId, {
    gestureHandling: true,
    zoom: 8,
    layers: [osm, EsriStreets, EsriImagery, EsriTopo],
    fullscreenControl: {
        pseudoFullscreen: false
    }
});

The Workaround: Providing a Fallback Center and Zoom Level

To ensure that users would see a meaningful map even if the primary center coordinates were delayed, I implemented a fallback mechanism. This involved setting default center coordinates and a default zoom level that would be used until the actual values were fetched.

Here’s how I modified the initialization code:

// Default center and zoom
const defaultCenter = [39.50, -98.35]; // Central USA
const defaultZoom = 4;

// Initialize the map with default center and zoom
view.map = L.map('map_' + mapId, {
    center: defaultCenter,
    zoom: defaultZoom,
    gestureHandling: true,
    layers: [osm, EsriStreets, EsriImagery, EsriTopo],
    fullscreenControl: {
        pseudoFullscreen: false
    }
});

// Update the map when the actual center is loaded
fetchLayer().then(layer => {
    const actualCenter = layer.getCenter();
    view.map.setView(actualCenter, 8);
});

Explanation:

I start by defining defaultCenter and defaultZoom with broadly applicable values. These defaults show a useful view (in this case, a central USA map overview) while users wait for more specific data. When the map is created, it now uses these defaults.

Once the layer data arrives, I use the setView method to update the center and zoom level of the map to focus on the intended region. The function fetchLayer() is a placeholder for whatever method you use to fetch your layer data.

Final Thoughts

Implementing a default view ensures that users are not faced with a blank screen if data layers load slowly. This approach significantly improves the user experience by making the interface feel quicker and more responsive. It also avoids potential confusion or frustration from end-users.

Always remember, in web development, especially in applications involving multiple external data sources, it’s essential to handle scenarios where data might not be immediately available. Using fallbacks or loading indicators ensures users know something is happening, enhancing their overall interaction with your app.