                    'mouseoversource': previousStyle.sources.mouseoversource,
                    'tracks': previousStyle.sources.tracks,
                    'selectedsource': previousStyle.sources.selectedsource,

                },
                layers: [
                    // background layer
                    ...nextStyle.layers,
                    previousStyle.layers.find(obj => obj.id === 'heatmap'),
                    previousStyle.layers.find(obj => obj.id === 'tracks-layer'),
              