> ## Documentation Index
> Fetch the complete documentation index at: https://docs.placematic.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Do I have to change my data model?

> Yes, in one specific way — and it's the way migrations fail. Design your abstraction from the richer capability set.

# 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.**

## The failure

<Warning>
  An interface derived from Google has no field for vehicle height. Or `access` point. Or per-field confidence.

  When you later add HERE, that data **has nowhere to live and gets silently dropped.**

  This is the most common structural error in Google-to-HERE migrations.
</Warning>

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.

## 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.

<Warning>
  **Vehicle constraints belong on the vehicle record, never at a call site.** A developer adding a new endpoint who copies a routing call without the profile has introduced a defect that is invisible in code review and returns `200`.
</Warning>

**Provider identifier in a nullable side column.** If cutting over wrote a `here_id` onto a core record, rollback becomes stateful. Keep it separable.

## 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.

## 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.

<Warning>
  Pass `4.1` to HERE and you have declared a four-centimetre truck. It routes under every bridge in North America. The response is `200`.
</Warning>

## 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.

## Related

<CardGroup cols={2}>
  <Card title="Google Migration Architecture" href="/architecture/google-migration-architecture">
    The provider facade, designed correctly.
  </Card>

  <Card title="Migrating One Endpoint" href="/examples/google-migration">
    Both adapters, side by side.
  </Card>

  <Card title="Routing System Architecture" href="/architecture/routing-system-architecture">
    Constraints live on records.
  </Card>

  <Card title="Address Validation" href="/use-cases/address-validation">
    Why `fieldScore` and `houseNumberType` must be persisted.
  </Card>
</CardGroup>

***

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