Update ArcGIS Online WebMap Extent Based on Polygon Feature Geometry with the ArcGIS API for Python
Introduction
The ArcGIS API for Python is a powerful Python library that allows users to interact with and automate tasks in ArcGIS Online (or Portal). The API is excellent for programmatically creating, maintaining, and updating webmaps in ArcGIS Online. If you have ever had to reset the extent of a WebMap after it has been let out in the wild for a while, then this workflow is for you. Here, we will focus in updating the extent for one WebMap, but you could certainly iterate through as many as required and update each extent individually as you go along. Please note, that this workflow is for the latest Map Viewer in ArcGIS Online (AGOL) and not for the Classic Viewer.
This blog post covers the workflow for version 2.4.0. For a comparison between early versions visit here.
Below is a WebMap zoomed to the extent of Ireland with some layers added. The original map extent focused on Galway over on the west coast. We will use to API to update/reset the map extent using the geometry of the polygon that represents Galway.
arcgis modules
Versions 2.4.0: The API provides access to your organisations ArcGIS Online via the GIS class in the gis module. This GIS class is the gateway to ArcGIS Online. We will need to import the Map class to create a Map object. The Map class is a part of the map module. This map module provides components for working with 2D and 3D maps and scenes. The Geometry class is imported from the geometry module. The geometry module defines useful geometry types and functions for working with geographic information and GIS functionality.
## import GIS which provides the gateway entry to your AGOL
from arcgis.gis import GIS
## import WebMap from the mapping module
from arcgis.map import Map
## import the Geometry class to get the bounding box for the extent
from arcgis.geometry import Geometry
Required Objects
Some required objects. The WebMap Item ID for the WebMap you want to update the extent for. The name of the layer as it appears in the WebMap that contains the polygon geometry for the extent. The SQL statement/where clause for limiting the polygon feature returned.
## the ITEM ID of the WebMap to update
wm_item_id = "WM_ITEM_ID"
## the layer name as it appears in the WebMap
lyr_name = "ENTER LYR NAME"
## the SQL clause to limit the geometry
sql_clause = "ENTER SQL CLAUSE"
Get Layer Index Function
A helper function to get the index of the layer of interest in the WebMap based on the layer name.
def getLayerIndexByName(wm_item, lyr_name):
try:
lyr_index = [index for index, lyr in enumerate(wm_item.get_data()["operationalLayers"]) if lyr["title"]==lyr_name][0]
return lyr_index
except IndexError:
return None
Accessing ArcGIS Online
## Access AGOL
agol = GIS("home")
## OR ##
## Access AGOL
agol = GIS(
url = "https://your_organisation.maps.arcgis.com/",
username = "Your_Username",
password = "Your_Password"
)
Create the Map Object
We first get the WebMap as an Item object and use that Item object to create a Map object.
## get the WebMap as an Item object
wm_item = agol.content.get(wm_item_id)
## create a WebMap object from the Item object
webmap = Map(wm_item)
Get the Bounding Box Information for the Feature of Interest
We get the index of the layer of interest in the WebMap and utilise the new MapContent layers property which will return a list of layers as FeatureLayer objects (only for non-grouped layers). We can then query the FeatureLayer and return the feature of interest. We then get the bounding box of the geometry for that feature.
## get the index for the layer in the webmap
lyr_index = getLayerIndexByName(wm_item, lyr_name)
## MapContent layers property returns a list of feature layers (or group layers)
fl = webmap.content.layers[lyr_index]
## Query the layer to return the feature you want to zoom to.
f = fl.query(where=sql_clause)
## get the minimum bounding of that feature as an envelope
bbox = Geometry(f.features[0].geometry).envelope
Update the WebMap Extent
Set the extent property for the Map object to the bounding box and update the Map object with the update() method to commit the change.
## update/add and initialState property to the WebMap
webmap.extent = bbox
## update the WebMap to reflect the new extent
webmap.update()
All the code in one place
You can find the entire code workflow below with links to important components in the documentation that were used. The code below is presented slightly different than the blog post.
from arcgis.gis import GIS
from arcgis.map import Map
from arcgis.geometry import Geometry
################################################################################
## API Reference Links:
## https://developers.arcgis.com/python/latest/api-reference/arcgis.gis.toc.html#gis
## https://developers.arcgis.com/python/latest//api-reference/arcgis.gis.toc.html#arcgis.gis.ContentManager.get
## https://developers.arcgis.com/python/latest/api-reference/arcgis.map.toc.html#map
## https://developers.arcgis.com/python/latest/api-reference/arcgis.map.toc.html#arcgis.map.Map.content
## https://developers.arcgis.com/python/latest/api-reference/arcgis.map.toc.html#mapcontent
## https://developers.arcgis.com/python/latest/api-reference/arcgis.map.toc.html#arcgis.map.map_widget.MapContent.layers
## https://developers.arcgis.com/python/api-reference/arcgis.features.toc.html#arcgis.features.FeatureLayer.query
## https://developers.arcgis.com/python/api-reference/arcgis.geometry.html
## https://developers.arcgis.com/python/api-reference/arcgis.geometry.html#geometry
## https://developers.arcgis.com/python/latest/api-reference/arcgis.map.toc.html#arcgis.map.Map.update
##
## Description:
## Update WebMap with a new Extent
##
## API Version: 2.4.0
##
################################################################################
################################################################################
## REQUIRED OBJECTS ############################################################
## the ITEM ID of the WebMap to update
wm_item_id = "WM_ITEM_ID"
## the layer name as it appears in the WebMap
lyr_name = "ENTER LYR NAME"
## the SQL clause to limit the geometry
sql_clause = "ENTER SQL CLAUSE"
################################################################################
## FUNCTIONS ###################################################################
def getLayerIndexByName(wm_item, lyr_name):
try:
lyr_index = [index for index, lyr in enumerate(wm_item.get_data()["operationalLayers"]) if lyr["title"]==lyr_name][0]
return lyr_index
except IndexError:
return None
################################################################################
## ACCESS AGOL #################################################################
agol = GIS("home")
################################################################################
## CREATE MAP OBJECT ###########################################################
## get the WebMap as an Item object
wm_item = agol.content.get(wm_item_id)
## create a WebMap object from the Item object
webmap = Map(wm_item)
################################################################################
## GET BOUNDING BOX INFO #######################################################
## get the index for the layer in the webmap
lyr_index = getLayerIndexByName(wm_item, lyr_name)
## MapContent layers property returns a list of feature layers (or group layers)
fl = webmap.content.layers[lyr_index]
## Query the layer to return the feature you want to zoom to.
f = fl.query(where=sql_clause)
## get the minimum bounding of that feature as an envelope
bbox = Geometry(f.features[0].geometry).envelope
################################################################################
## UPDATE THE EXTENT ###########################################################
## update/add and initialState property to the WebMap
webmap.extent = bbox
## update the WebMap to reflect the new extent
webmap.update()
################################################################################
