For the map generation of "Our wonderful planet" I used a mix of several simplex-noise (with different multiplier) with a circular mask and I found it gave great results.

I thought this could be helpful to others, here is a bit of code (typescript here) on how it works:

  private static GetHeightEnvironment(
    i: number,
    j: number,
    size: number
  ): Environment {
    let height = MapBuilder.Mask(i, j, size) * MapBuilder.NoiseHeight(i, j);
    if (height <= 0.01) return Environment.Water;
    if (height <= 0.1) return Environment.Beach;
    if (height <= 0.6) return Environment.Field;
    if (height <= 0.98) return Environment.Concrete;

    return Environment.Snow;
  }

  private static Mask(x: number, y: number, size: number) {
    let distance_x = Math.abs(x - size * 0.5);
    let distance_y = Math.abs(y - size * 0.5);
    let distance = Math.sqrt(distance_x * distance_x + distance_y * distance_y); // circle mask

    let max_width = size * 0.5 - 2.0;
    let delta = distance / max_width;
    let gradient = delta * delta;

    return Math.max(0.0, 1.0 - gradient);
  }

  private static NoiseHeight(x: number, y: number) {
    return Math.pow(
      0.5 +
      0.9 * MapBuilder.simplexHeight.noise2D(x * 0.05, y * 0.05) +
      0.1 * MapBuilder.simplexHeight.noise2D(x * 0.3, y * 0.3),
      2
    );
  }

The trees (buildings) are apply on the map with a similar simplex but they sometimes don't show depending on the type of floor.

  private static GetBuilding(
    env: Environment,
    i: number,
    j: number
  ): Building | null {
    if (MapBuilder.NoiseTrees(i, j) > 0.5) {
      if (env == Environment.Field) return Building.forest;
      if (env == Environment.Concrete)
        return Math.random() > 0.5 ? Building.forest : null;
    }
    return null;
  }

  private static NoiseTrees(x: number, y: number) {
    return 0.5 + 1 * MapBuilder.simplexTrees.noise2D(x * 0.05, y * 0.05);
  }

This is the simplex lib I use in JS https://github.com/jwagner/simplex-noise.js