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PathLayer

Screenshot from North America roads example

lonboard.PathLayer

Bases: BaseArrowLayer

The PathLayer renders lists of coordinate points as extruded polylines with mitering.

Example:

From GeoPandas:

import geopandas as gpd
from lonboard import Map, PathLayer

# A GeoDataFrame with LineString or MultiLineString geometries
gdf = gpd.GeoDataFrame()
layer = PathLayer.from_geopandas(
    gdf,
    get_color=[255, 0, 0],
    width_min_pixels=2,
)
m = Map(layer)

From an Arrow-compatible source like pyogrio or geoarrow-rust:

from geoarrow.rust.io import read_flatgeobuf
from lonboard import Map, PathLayer

# Example: A FlatGeobuf file with LineString or MultiLineString geometries
table = read_flatgeobuf("path/to/file.fgb")
layer = PathLayer(
    table,
    get_color=[255, 0, 0],
    width_min_pixels=2,
)
m = Map(layer)

auto_highlight 

auto_highlight = Bool(default_value=False)

When true, the current object pointed to by the mouse pointer (when hovered over) is highlighted with highlightColor.

Requires pickable to be True.

  • Type: bool
  • Default: False

before_id 

before_id = Unicode(None, allow_none=True)

The identifier of a layer in the Maplibre basemap layer stack.

This deck.gl layer will be rendered just before the layer with the given identifier. You can find such an identifier by inspecting the basemap style JSON.

For example, in the Carto Positron style, if you look at the raw JSON data, each layer has an "id" property. The first layer in the basemap stack has "id": "background". So if you pass before_id="background", you won't see your deck.gl layer because it will be rendered below all layers in the Maplibre basemap.

A common choice for Carto-based styles is to use before_id="watername_ocean" so that your deck.gl layer is rendered above the core basemap elements but below all text labels.

Info

This only has an effect when the map's basemap is a MaplibreBasemap, and the map is rendering in "interleaved" mode.

billboard 

billboard = Bool(None, allow_none=True)

If True, extrude the path in screen space (width always faces the camera). If False, the width always faces up.

  • Type: bool, optional
  • Default: False

cap_rounded 

cap_rounded = Bool(None, allow_none=True)

Type of caps. If True, draw round caps. Otherwise draw square caps.

  • Type: bool, optional
  • Default: False

extensions 

extensions = tag(sync=True, **(widget_serialization))

A list of layer extension objects to add additional features to a layer.

get_color 

get_color = ColorAccessor(None, allow_none=True)

The color of each path in the format of [r, g, b, [a]]. Each channel is a number between 0-255 and a is 255 if not supplied.

  • Type: ColorAccessor, optional
    • If a single list or tuple is provided, it is used as the color for all paths.
    • If a numpy or pyarrow array is provided, each value in the array will be used as the color for the path at the same row index.
  • Default: [0, 0, 0, 255].

get_width 

get_width = FloatAccessor(None, allow_none=True)

The width of each path, in units specified by width_units (default 'meters').

  • Type: FloatAccessor, optional
    • If a number is provided, it is used as the width for all paths.
    • If an array is provided, each value in the array will be used as the width for the path at the same row index.
  • Default: 1.

highlight_color 

highlight_color = VariableLengthTuple(
    Int(), default_value=(0, 0, 128, 128), minlen=3, maxlen=4
)

RGBA color to blend with the highlighted object (the hovered over object if auto_highlight=true). When the value is a 3 component (RGB) array, a default alpha of 255 is applied.

  • Type: List or Tuple of integers
  • Default: [0, 0, 128, 128]

joint_rounded 

joint_rounded = Bool(None, allow_none=True)

Type of joint. If True, draw round joints. Otherwise draw miter joints.

  • Type: bool, optional
  • Default: False

miter_limit 

miter_limit = Int(None, allow_none=True)

The maximum extent of a joint in ratio to the stroke width. Only works if jointRounded is False.

  • Type: float, optional
  • Default: 4

opacity 

opacity = Float(1, min=0, max=1)

The opacity of the layer.

  • Type: float. Must range between 0 and 1.
  • Default: 1

pickable 

pickable = Bool(default_value=True)

Whether the layer responds to mouse pointer picking events.

This must be set to True for tooltips and other interactive elements to be available. This can also be used to only allow picking on specific layers within a map instance.

Note that picking has some performance overhead in rendering. To get the absolute best rendering performance with large data (at the cost of removing interactivity), set this to False.

  • Type: bool
  • Default: True

selected_index 

selected_index = Int(None, allow_none=True)

The positional index of the most-recently clicked on row of data.

You can use this to access the full row of data from a GeoDataFrame

gdf.iloc[layer.selected_index]

Setting a value here from Python will do nothing. This attribute only exists to be updated from JavaScript on a map click. Note that pickable must be True (the default) on this layer for the JavaScript onClick handler to work; if pickable is set to False, selected_index will never update.

Note that you can use observe to call a function whenever a new value is received from JavaScript. Refer here for an example.

table 

table = ArrowTableTrait(allowed_geometry_types={LINESTRING, MULTILINESTRING})

A GeoArrow table with a LineString or MultiLineString column.

This is the fastest way to plot data from an existing GeoArrow source, such as geoarrow-rust or geoarrow-pyarrow.

If you have a GeoPandas GeoDataFrame, use from_geopandas instead.

visible 

visible = Bool(default_value=True)

Whether the layer is visible.

Under most circumstances, using the visible attribute to control the visibility of layers is recommended over removing/adding the layer from the Map.layers list.

In particular, toggling the visible attribute will persist the layer on the JavaScript side, while removing/adding the layer from the Map.layers list will re-download and re-render from scratch.

  • Type: bool
  • Default: True

width_max_pixels 

width_max_pixels = Float(None, allow_none=True, min=0)

The maximum path width in pixels. This prop can be used to prevent the path from getting too thick when zoomed in.

  • Type: float, optional
  • Default: None

width_min_pixels 

width_min_pixels = Float(None, allow_none=True, min=0)

The minimum path width in pixels. This prop can be used to prevent the path from getting too thin when zoomed out.

  • Type: float, optional
  • Default: 0

width_scale 

width_scale = Float(None, allow_none=True, min=0)

The path width multiplier that multiplied to all paths.

  • Type: float, optional
  • Default: 1

width_units 

width_units = Unicode(None, allow_none=True)

The units of the line width, one of 'meters', 'common', and 'pixels'. See unit system.

  • Type: str, optional
  • Default: 'meters'

__init__ 

__init__(
    table: ArrowStreamExportable,
    *,
    _rows_per_chunk: int | None = None,
    **kwargs: Unpack[PathLayerKwargs]
) -> None

Construct a Layer from a GeoArrow table.

This accepts Arrow data from any library implementing the Arrow PyCapsule Interface, including pyarrow, arro3, DuckDB, and others.

The geometry column will be reprojected to EPSG:4326 if it is not already in that coordinate system.

Parameters:

  • table (ArrowStreamExportable) –

    An Arrow table or stream object from a library implementing the [Arrow PyCapsule Interface]. This object must contain a column with a geometry type that has the geoarrow extension metadata.

Other Parameters:

  • kwargs (Unpack[BaseLayerKwargs]) –

    parameters passed on to __init__

Returns:

  • None –

    A Layer with the initialized data.

from_duckdb 

from_duckdb(
    sql: str | DuckDBPyRelation,
    con: DuckDBPyConnection | None = None,
    *,
    crs: str | CRS | None = None,
    **kwargs: Unpack[PathLayerKwargs]
) -> Self

Construct a Layer from a duckdb-spatial query.

With DuckDB >= 1.5, the CRS of a GEOMETRY column is read automatically from the column type (e.g. GEOMETRY('EPSG:3857')) and the data is reprojected to EPSG:4326 as needed.

The crs keyword parameter is deprecated for such input and is only needed when the data cannot describe its own CRS: WKB_BLOB or 2D columns (POINT_2D, LINESTRING_2D, POLYGON_2D, BOX_2D), DuckDB older than 1.5, or a GEOMETRY column without a CRS encoded. In those cases, the user must ensure that data has been reprojected to EPSG:4326 or pass the existing CRS of the data in the crs keyword parameter.

Parameters:

  • sql (str | DuckDBPyRelation) –

    The SQL input to visualize. This can either be a string containing a SQL query or the output of the duckdb sql function.

  • con (DuckDBPyConnection | None, default: None ) –

    The current DuckDB connection. This is required when passing a str to the sql parameter.

Other Parameters:

  • crs (str | CRS | None) –

    The CRS of the input data, for input that cannot describe its own CRS (see above). This can either be a string passed to pyproj.CRS.from_user_input or a pyproj.CRS object. Errors if it conflicts with the CRS encoded in a DuckDB >= 1.5 GEOMETRY column. Defaults to None.

  • kwargs (Unpack[BaseLayerKwargs]) –

    parameters passed on to __init__

Returns:

  • Self –

    A Layer with the initialized data.

from_geopandas 

from_geopandas(
    gdf: GeoDataFrame,
    *,
    auto_downcast: bool = True,
    **kwargs: Unpack[PathLayerKwargs]
) -> Self

Construct a Layer from a geopandas GeoDataFrame.

The GeoDataFrame will be reprojected to EPSG:4326 if it is not already in that coordinate system.

Parameters:

  • gdf (GeoDataFrame) –

    The GeoDataFrame to set on the layer.

Other Parameters:

  • auto_downcast (bool) –

    If True, automatically downcast to smaller-size data types if possible without loss of precision. This calls pandas.DataFrame.convert_dtypes and pandas.to_numeric under the hood.

  • kwargs (Unpack[BaseLayerKwargs]) –

    parameters passed on to __init__

Returns:

  • Self –

    A Layer with the initialized data.