def stitch_map(tiles, width, height, bbox, dpi):
    """
    Merge tiles together into one image.

    Args:
        tiles (list of dict of file): tiles for each layer
        width (float): page width in mm
        height (height): page height in mm
        dpi (dpi): resolution in dots per inch

    Returns:
        PIL.Image: merged map.

    """
    size = (int(width * dpi_to_dpmm(dpi)), int(height * dpi_to_dpmm(dpi)))
    background = Image.new('RGBA', size, (255, 255, 255))
    for layer in tiles:
        layer_img = Image.new("RGBA", size)
        for (x, y), tile_path in layer.items():
            tile = Image.open(tile_path)
            layer_img.paste(tile, ((x - bbox.min.x) * TILE_SIZE, (y - bbox.min.y) * TILE_SIZE))
        background = Image.alpha_composite(background, layer_img)
    add_scales_bar(background, bbox)
    return background.convert("RGB")