Merge pull request #2215 from felixniemeyer/patch-1

adding example for multiple disconnected lines

Author: nicolaskruchten

doc/python/lines-on-maps.md

@@ -111,6 +111,80 @@ fig.update_layout(
 
 fig.show()
 ```
+### Performance improvement: put many lines in the same trace
+For very large amounts (>1000) of lines, performance may become critcal. If you can relinquish setting individual line styles (e.g. opacity), you can put multiple paths into one trace. This makes the map render faster and reduces the script execution time and memory consumption. 
+
+Use ```None``` between path coordinates to create a break in the otherwise connected paths. 
+
+```python 
+import plotly.graph_objects as go
+import pandas as pd
+
+df_airports = pd.read_csv('https://raw.githubusercontent.com/plotly/datasets/master/2011_february_us_airport_traffic.csv')
+df_airports.head()
+
+df_flight_paths = pd.read_csv('https://raw.githubusercontent.com/plotly/datasets/master/2011_february_aa_flight_paths.csv')
+df_flight_paths.head()
+
+fig = go.Figure()
+
+fig.add_trace(go.Scattergeo(
+    locationmode = 'USA-states',
+    lon = df_airports['long'],
+    lat = df_airports['lat'],
+    hoverinfo = 'text',
+    text = df_airports['airport'],
+    mode = 'markers',
+    marker = dict(
+        size = 2,
+        color = 'rgb(255, 0, 0)',
+        line = dict(
+            width = 3,
+            color = 'rgba(68, 68, 68, 0)'
+        )
+    )))
+
+flight_paths = []
+lons = []
+lats = []
+import numpy as np
+lons = np.empty(3 * len(df_flight_paths))
+lons[::3] = df_flight_paths['start_lon']
+lons[1::3] = df_flight_paths['end_lon']
+lons[::3] = None
+lats = np.empty(3 * len(df_flight_paths))
+lats[::3] = df_flight_paths['start_lat']
+lats[1::3] = df_flight_paths['end_lat']
+lats[::3] = None
+
+fig.add_trace(
+    go.Scattergeo(
+        locationmode = 'USA-states',
+        lon = lons,
+        lat = lats,
+        mode = 'lines',
+        line = dict(width = 1,color = 'red'),
+        opacity = 0.5 
+    )
+)
+
+fig.update_layout(
+    title_text = 'Feb. 2011 American Airline flight paths<br>(Hover for airport names)',
+    showlegend = False,
+    geo = go.layout.Geo(
+        scope = 'north america',
+        projection_type = 'azimuthal equal area',
+        showland = True,
+        landcolor = 'rgb(243, 243, 243)',
+        countrycolor = 'rgb(204, 204, 204)',
+    ),
+    height=700,
+)
+
+fig.show()
+
+```
+
 
 ### London to NYC Great Circle