Draw polygon in mapbox with dash/python

Dash Python
5

Hi @anjulia

You can draw polygons in lon- lat coordinates, defined asmapbox layers.
Here is an example of recatngular shape over Sweden:

import plotly.graph_objs as go
mapbox_t=open(".mapbox_token").read().rstrip()
data = [go.Scattermapbox(
                    lat=[62.3833], # [57.671667] ,
                    lon=[16.3000], # [11.980833],
                    mode='markers',
                    marker=dict(
                            size= 3,
                            color = 'red',
                            opacity = .8,
                            ))]
#set the layout to plot
layout = go.Layout(autosize=True,
                   mapbox = dict(center= dict(lat=62.3833,     #Set center at Flataklocken
                                 lon=16.3000),        
                                 accesstoken=mapbox_t,
                                 zoom=4,
                                 style='light',
                               ),
                   
                    width=700,
                    height=600,
                    title = 'Sweden')
fig = go.Figure(data=data, layout=layout)

The following function defines a geojson-type dict corresponding to each polygon, no matter how many vertices it has:

def get_polygon(lons, lats, color='blue'):
    if len(lons) != len(lats):
        raise ValueError('the legth of longitude list  must coincide with that of latitude')
    geojd = {"type": "FeatureCollection"}
    geojd['features'] = []
    coords = []
    for lon, lat in zip(lons, lats): 
        coords.append((lon, lat))   
    coords.append((lons[0], lats[0]))  #close the polygon  
    geojd['features'].append({ "type": "Feature",
                               "geometry": {"type": "Polygon",
                                            "coordinates": [coords] }})
    layer=dict(sourcetype = 'geojson',
             source =geojd,
             below='',  
             type = 'fill',   
             color = color)
    return layer

Now let us define a simple polygon:

mylayers =[]
mylayers.append(get_polygon(lons=[14, 16, 16, 14], lats=[58.55, 58.55, 60.6, 60.6],  color='gold'))
fig.layout.update(mapbox_layers =mylayers);

sweden-polyg
sweden-polyg700×600 89.1 KB

Unfortunately we cannot plot polygons only inside th Goteborg boundaries, because they have very small lengths (less than 1 degree), and plotly cannot draw polygons of such a small area. No error message is displayed, but the polygons are invisible.

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