A map is not the world state

827. Lesson identity

Module

2.12 — Navigation, maps, and vehicles

Lesson

A map is not the world state

Academic type

Systems

Schema type

Text

Order

1 in the module

Estimated time

30–40 minutes, including practice

828. Learning objective

After this lesson, you can define a navigation contract for a bounded route by separating spatial representation, destination intent, movement conditions, arrival evaluation, and the contract owner’s permitted transitions.

829. Why this matters

A map describes where locations and routes are represented; it does not decide what the world currently permits. A destination is an intent, not proof that an actor has arrived. If these ideas are combined, a vehicle can appear to reach a marker while its route is blocked, its intent is stale, or its movement does not satisfy the declared arrival rule.

A bounded contract makes each decision inspectable: which system holds the destination, which observations are used to evaluate arrival, and which system may change the navigation state.

830. Prior knowledge

You should already be able to bound a world behavior using one owner, limited state, permitted transitions, and observable consequences. This lesson builds on 2.10 L2 — Bound the world requirement. You do not need to implement a map, vehicle, or pathfinding system.

831. Core concept

A navigation design has three distinct input concerns:

1. Spatial representation: coordinates, bounds, route geometry, obstacles, and landmarks.
2. Movement state: the actor’s position, motion, operational condition, and current movement permissions.
3. Destination intent: the destination or route the actor is currently meant to follow.

A fourth element surrounds those inputs: the bounded navigation contract. The contract declares its owner, accepted observations, permitted transitions, and observable results. It is not another map layer and is not interchangeable with a destination marker.

A map can contain a destination marker without making the destination reachable. An active destination does not authorize movement. Matching a destination coordinate does not establish arrival unless the declared arrival conditions are also satisfied.

For a bounded route, specify:

• the system that owns the navigation attempt and active destination intent;
• the coordinate frame, distance metric, units, and valid route bounds;
• the destination representation;
• the movement and world-state conditions that permit or block progress;
• the evaluator that observes arrival inputs;
• the arrival criteria and reported result;
• the transitions the owner may perform after accepting that report;
• the observable results for completion, blockage, cancellation, or failure.

832. Ownership and arrival evaluation

The navigation owner holds the active destination intent and owns the contract state. Only that owner performs the contract’s declared transitions.

The arrival evaluator observes declared inputs. In this lesson’s model, those inputs are:

• the actor position and destination position in the same coordinate frame;
• distance between those positions, measured with the declared metric and units;
• actor speed in declared units;
• route validity, including whether the route is open;
• the actor’s operational condition.

The evaluator reports whether the arrival criteria are met. It does not silently replace the destination, cancel the route, or complete the contract. The navigation owner accepts the report and performs only a declared transition, such as active to complete. This evaluator may be implemented inside or outside the owning system; the important boundary is that observation does not acquire authority merely because it produced a result.

833. Mental model

Use three input concerns plus one bounded contract:

The first three elements supply distinct inputs. The bounded contract determines how the owner may interpret their reports. Map data can locate a destination without owning the intent. Movement state can report that a vehicle is stopped without completing the route. The arrival evaluator can report that criteria are met without gaining authority to change the contract.

Ask these questions in order:

1. What coordinate frame, units, bounds, and route facts exist?
2. What is the actor doing, and what permits or blocks movement?
3. Which destination intent does the navigation owner currently hold?
4. What does the arrival evaluator observe and report?
5. Which transition may the navigation owner perform for that report?

834. Worked example

Consider a vehicle traveling from river_crossing to north_outpost.

A weak rule says, “When the vehicle reaches the north-outpost marker, the route is complete.” It does not define the coordinate frame, units, stopping rule, route validity, evaluator, or state authority.

The following bounded contract uses explicit design decisions. The values are examples, not universal constants:

• Navigation owner: the active vehicle navigation controller.
• Contract states: active, blocked, cancelled, failed, and complete.
• Map and bounds: the declared route from river_crossing to north_outpost within its valid route region.
• Coordinate decision: current vehicle position and destination position are both expressed in the same world-space frame.
• Measurement decision: straight-line distance is measured in world-space meters.
• Destination intent: travel to north_outpost while the intent remains active.
• Progress permission: movement is permitted only while the vehicle is operational and the route is open.
• Arrival evaluator inputs: vehicle position, destination position, vehicle speed, route validity, and operational condition.
• Arrival thresholds: distance to the destination is at or below 2 m, speed is at or below 0.2 m/s, the route is open and valid, and the vehicle is operational.
• Evaluator output: arrival-criteria-met or arrival-criteria-not-met for the current evaluation.
• Success transition: when the owner receives arrival-criteria-met for its current active intent, it changes active to complete and exposes north_outpost as the completed destination.
• Blocked transition: if the route becomes blocked while the intent is active, the owner changes active to blocked; proximity does not override this result.

The distance comparison is meaningful because both positions use the same coordinate frame, metric, and units. A vehicle 1.5 m from the destination but moving at 1.0 m/s does not meet this contract’s arrival criteria. A stopped vehicle within 2 m also does not qualify if the route is blocked, invalid, or no longer belongs to the current intent.

The marker may display north_outpost, but it neither evaluates arrival nor changes the navigation state.

835. Common mistakes

836. Treating a marker as authority

A marker is spatial or presentation data. It may be hidden, decorative, stale, or associated with a cancelled intent. Its visibility or overlap does not prove arrival.

837. Comparing incompatible coordinates

A distance has no reliable contract meaning if the actor and destination positions use different frames, metrics, or units. Convert them into a declared compatible frame before applying a tolerance.

838. Letting the evaluator own transitions

An evaluator reports observations. The navigation owner decides whether the report belongs to the current intent and performs only a permitted transition. This prevents a late report for an old destination from completing a newer route.

839. Collapsing navigation into a “map system”

This hides whether a defect belongs to representation, intent, movement permission, arrival evaluation, or state transition. Keep those responsibilities named and bounded.

840. Guided practice

Draft a navigation contract for this scenario:

A vehicle must travel from camp to checkpoint. The checkpoint appears on the map, the vehicle can become disabled, and the route can become blocked. The route completes only when the vehicle is sufficiently close to the checkpoint and has stopped.

Complete the table:

Then draw a four-part diagram with separate boxes for map data, movement state, destination intent, and the bounded contract. Label these flows:

1. map and movement observations enter the arrival evaluator;
2. the evaluator reports whether the criteria are met;
3. the navigation owner checks that the report belongs to the current intent;
4. the owner performs a declared transition.

Finally, decide what happens in each case and justify it using your contract:

• the vehicle enters the distance tolerance while still above the speed threshold;
• the route becomes blocked while the vehicle is near the checkpoint;
• the destination changes before a report for the old destination is accepted;
• actor and destination positions arrive in incompatible coordinate frames.

841. Validation and evidence

Your evidence consists of the completed contract table and four-part diagram. Another developer should be able to determine without guessing:

1. which system owns the destination intent and contract state;
2. which component observes and evaluates arrival;
3. which compatible coordinate frame, metric, and units support the distance test;
4. which movement and route conditions permit arrival;
5. what the evaluator reports;
6. which transitions the owner may perform for completion, blockage, cancellation, or failure;
7. why the map marker is not authoritative world state.

842. Key takeaways

• A map represents spatial information; it does not own navigation truth.
• Destination intent states where the actor is meant to go; it does not prove arrival.
• Movement and route validity remain separate inputs.
• An arrival evaluator observes declared inputs and reports a result.
• The navigation owner holds the intent, accepts relevant reports, and performs only declared transitions.
• Distance tolerances require compatible coordinate frames, metrics, and units.

843. Next lesson

Continue to 2.12 L2 — Vehicle possession is a state handoff. The next lesson applies the same ownership discipline when input and movement authority pass between player and vehicle during entry, exit, or interruption; the map, destination marker, and vehicle presentation do not become authoritative merely because control changes.

844. Knowledge check