Part 6 - Utility functions for the map widget¶
In this notebook, we will explore using utility functions to build interactivity. This can usually be split into two procedures:
call back and
display message. The
call back function can be used to collect
gis data on screen through digitization, while the
display message function can be used to prompt users to perform a desired action.
To do this, we will need to setup an asynchronous
callback function using the
on_draw_end() methods to create dynamic, interactive 'apps'. We will need to create a
callback function, like
function_name(map_inst, geometry), with map_inst being the
MapView instance and geometry being the geometry instance that the user is clicking.
Demonstrate callback features with
Our first example will take a point that a user clicks on the map, reverse geocode it from the geometry, and print out the resulting location.
Note, you can either create the
GIS connection using an existing profile, or you can simply enter your username and password, e.g.
gis = GIS("https://www.arcgis.com", "username", "password").
from arcgis.gis import GIS import arcgis.geocoding as geocoding gis = GIS('home') callback_map = gis.map('San Diego convention center, San Diego, CA', 16)
def find_addr(callback_map, g): try: callback_map.draw(g) geocoded = geocoding.reverse_geocode(g) print(geocoded['address']['Match_addr']) except: print("Couldn't match address. Try another place...")
Next, we want a user to draw a freehand
polyline to indicate the paths they take for their runs. When the drawing operation ends, we use the
GIS's Geometry service to compute the length of the drawn path. We can do this by adding an event listener to the map widget that gets called when drawing is completed (i.e.
on_draw_end). The event listener then computes the geodesic length of the drawn geometry using the geometry service and prints it out:
drawend_map = gis.map('San Diego convention center, San Diego, CA', 16)
from arcgis.geometry import lengths # Define the callback function that computes the length. def calc_dist(drawend_map, g): print("Computing length of drawn polyline...") length = lengths(g['spatialReference'], [g], "", "geodesic") print("Length: " + str(length) + " mile(s).")
# Set calc_dist as the callback function to be invoked when a polyline is drawn on the map drawend_map.on_draw_end(calc_dist) drawend_map
Show message in map widget via
display_message method displays a message on the upper-right corner of the map widget.