QGIS/resources/function_help/json/overlay_nearest

{
  "name": "overlay_nearest",
  "type": "function",
  "groups": ["GeometryGroup"],
  "description": "Returns whether the current feature has feature(s) from a target layer within a given distance, or an array of expression-based results for the features in the target layer within a distance from the current feature.<br><br>Note: This function can be slow and consume a lot of memory for large layers.",
  "arguments": [
    {
      "arg": "layer",
      "description": "the target layer"
    },
    {
      "arg": "expression",
      "description": "an optional expression to evaluate on the features from the target layer. If not set, the function will just return a boolean indicating whether there is at least one match.",
      "optional": true
    },
    {
      "arg": "filter",
      "description": "an optional expression to filter the target features to check. If not set, all the features in the target layer will be used.",
      "optional": true
    },
    {
      "arg": "limit",
      "description": "an optional integer to limit the number of matching features. If not set, only the nearest feature will be returned. If set to -1, returns all the matching features.",
      "optional": true,
      "default": "1"
    },
    {
      "arg": "max_distance",
      "description": "an optional distance to limit the search of matching features. If not set, all the features in the target layer will be used.",
      "optional": true
    },
    {
      "arg": "cache",
      "description": "set this to true to build a local spatial index (most of the time, this is unwanted, unless you are working with a particularly slow data provider)",
      "optional": true,
      "default": "false"
    }
  ],
  "examples": [
    {
      "expression": "overlay_nearest('airports')",
      "returns": "true if the \"airports\" layer has at least one feature"
    },
    {
      "expression": "overlay_nearest('airports', max_distance:= 5000)",
      "returns": "true if there is an airport within a distance of 5000 map units from the current feature"
    },
    {
      "expression": "overlay_nearest('airports', name)",
      "returns": "the name of the closest airport to the current feature, as an array"
    },
    {
      "expression": "array_to_string(overlay_nearest('airports', name))",
      "returns": "the name of the closest airport to the current feature, as a string"
    },
    {
      "expression": "overlay_nearest(layer:='airports', expression:= name, max_distance:= 5000)",
      "returns": "the name of the closest airport within a distance of 5000 map units from the current feature, as an array"
    },
    {
      "expression": "overlay_nearest(layer:='airports', expression:=\"name\", filter:= \"Use\"='Civilian', limit:=3)",
      "returns": "an array of names, for up to the three closest civilian airports ordered by distance"
    },
    {
      "expression": "overlay_nearest(layer:='airports', expression:=\"name\", limit:= -1, max_distance:= 5000)",
      "returns": "an array of names, for all the airports within a distance of 5000 map units from the current feature, ordered by distance"
    }
  ]
}