Same again, I find interpolation more semantic, I know I am dealing with Strings, the `+` operator is so overloaded that interpolation seems less risky to me.

This is quite similar to the above so perhaps can be extracted into a method

```
def _getLayerBoundingBox(layer) {

    def minX = layer.bboxMinX.toDouble()
    if(layer.bboxMinX == layer.bboxMaxX) {
	minX -= 1
    }

    def minY = layer.bboxMinY.toDouble()
    if(layer.bboxMinY == layer.bboxMaxY) {
	minY -= 1;
    }

    return "${minX},${minY},${layer.bboxMaxX},$layer.bboxMaxY}"
}
```

These sections look similar perhaps another method could be extraced? 
```
def minX = layer.bboxMinX.toDouble()
if(layer.bboxMinX == layer.bboxMaxX) {
    minX -= 1
}

def minY = layer.bboxMinY.toDouble()
if(layer.bboxMinY == layer.bboxMaxY) {
    minY -= 1;
}
```