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Do I have to change my data model?

Short answer: Not much, except in one place that matters enormously. If you build a provider facade, design its interface from HERE’s capability set, not Google’s.

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The failure

If your Google implementation had no notion of a vehicle’s physical dimensions — because Google could not express them — an interface abstracted from it has no field for one. The route still returns 200. The truck still gets dispatched.

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What to add

access point. HERE returns two coordinates per geocode: position (the address) and access (where a vehicle arrives on the road network). Google returns one. Route to access. Routing to position may target a building’s geometric centre, or a point separated from the road by a car park. Per-field confidence. HERE returns queryScore and fieldScore — which component was uncertain. queryScore: 0.95 with fieldScore.houseNumber: 0.4 is a failed delivery. fieldScore.postalCode: 0.8 is not. Rooftop vs interpolated. houseNumberType: "PA" is a surveyed point address. interpolated is an estimate along a street segment, potentially tens of metres off. Vehicle profile as a first-class record. Height (centimetres), gross weight (kilograms), axle count including trailers, hazmat cargo types, ADR tunnel category. Provider identifier in a nullable side column. If cutting over wrote a here_id onto a core record, rollback becomes stateful. Keep it separable.

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What doesn’t change

Your PostGIS geometry. Your delivery zones. Your geocode cache table. Your geofence polygons. Most of what a location system does never touches a location API. That layer is identical on either platform.

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Convert units at the adapter

Not in the interface. HERE’s height is centimetres. TomTom’s vehicleHeight is metres. Store one, and make each adapter responsible for the conversion.

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Common misconceptions

“We’ll add the fields when we need them.” You need them at the moment you dispatch a truck, and by then the interface has fifty call sites. “Confidence is just a number.” Storing a coordinate without its confidence converts a probabilistic estimate into a fact. Every downstream system treats it as truth. Low-confidence fallbacks silently corrupt revenue maps and route vehicles to centroids. “The facade should be minimal.” The facade should express every constraint that determines whether a route is legal.

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Related

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