[
  {
    "id": 1, 
    "name": "Urban Extent", 
    "sub_themes": [
      {
        "categories": [
          {
            "id": 1
          }, 
          {
            "id": 2, 
            "name": "Population", 
            "unit": "(thousands)"
          }, 
          {
            "id": 3, 
            "name": "Population density", 
            "unit": "(people per sq. km.)"
          }
        ], 
        "id": 1, 
        "name": "Administrative"
      }, 
      {
        "categories": [
          {
            "id": 4, 
            "name": "Area", 
            "unit": "(sq. km.)"
          }, 
          {
            "id": 5,
            "name": "Population", 
            "unit": "(thousands)"
          }, 
          {
            "id": 6, 
            "name": "Population density", 
            "unit": "(people per sq. km.)"
          }
        ], 
        "id": 2, 
        "name": "Built up"
      }]
  }
]