spatial-etl-framework

JSONPath Query Conventions

The line:

query: "$.features[*].properties.urls.pbf"

is written in JSONPath convention. JSONPath is to JSON what XPath is to XML → a mini “query language” to navigate nested structures.

---

🔹 JSONPath Building Blocks

1. $ → root object

• Always starts at the very top.\
• Equivalent to “the whole JSON document”.

{ "foo": 123 }

• $ = the whole object
• $.foo = 123

---

2. . → child operator

• Dot-notation to access an object’s property.

{ "a": { "b": 42 } }

• $.a = { "b": 42 }
• $.a.b = 42

---

3. [*] → wildcard array

• Selects all elements of an array.

{ "nums": [10, 20, 30] }

• $.nums[*] = [10, 20, 30]

---

4. .. → recursive descent

• Search at any depth (like ** in globbing).

{ "foo": { "bar": { "baz": 99 } } }

• $..baz = 99

---

5. [] → array index / slice / filter

• [0] → first item\
• [1:3] → slice\
• [?(@.key=="value")] → filter

Example:

{
  "users": [
    {"id": 1, "role": "admin"},
    {"id": 2, "role": "user"}
  ]
}

• $.users[0].id = 1\
• $.users[*].role = ["admin", "user"]\
• $.users[?(@.role=="admin")].id = [1]

---

6. @ → current object

Used inside filters.

---

🔹 Your Query Explained

query: "$.features[*].properties.urls.pbf"

Applied to your GeoJSON:

{
  "features": [
    {
      "properties": {
        "urls": {
          "pbf": "https://download.geofabrik.de/asia/afghanistan-latest.osm.pbf"
        }
      }
    },
    {
      "properties": {
        "urls": {
          "pbf": "https://download.geofabrik.de/asia/india-latest.osm.pbf"
        }
      }
    }
  ]
}

Step by step:

1. $ → start at root object\
2. .features → go into the features array\
3. [*] → take every element in that array\
4. .properties.urls.pbf → drill down into properties → urls → pbf

👉 Result = list of all PBF download URLs:

[
  "https://download.geofabrik.de/asia/afghanistan-latest.osm.pbf",
  "https://download.geofabrik.de/asia/india-latest.osm.pbf"
]

---

🔑 Summary of JSONPath Conventions

• $ = root\
• . = child\
• [*] = all items in array\
• [0], [1:3] = array index/slice\
• ?() = filter with condition\
• @ = current object\
• .. = recursive descent (all levels)

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