Given a web map, it is mixed of a bunch of feature layers, map image layers, image layers.
each of these layers has its own source.
Normally, you can click the link for each layer, it will open up where this layer comes from.
Usually, feature layers can come from portal item, can come directly from arcgis server REST api URL,
Generally speaking, you can click each layer's link to dig out the source of this feature layer.
What if a feature layer has no link, how you find out where this feature layer comes from
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