Explain the concept of 'Localization' in autonomous vehicles and why it's critical.

Example answer

Localization estimates a vehicle's position and orientation relative to a coordinate frame, together with uncertainty. Navigation and local planning need this estimate to relate observations, road geometry and intended motion. It is not an exact position or a universal centimetric-accuracy guarantee.

Depending on the design, GNSS, inertial measurements, wheel motion, cameras, radar, LiDAR and maps may contribute. Relative motion estimates can drift; global observations or map matches can reduce some uncertainty but can also be biased, stale or ambiguous. SLAM estimates motion and a map together; it does not make every map feature correct.

Evaluate accuracy, integrity and data age for the intended domain. Check difficult geometry, GNSS blockage or multipath, changed map features, calibration errors and timing inconsistencies. An apparently precise estimate can be wrong if its uncertainty model omits these failures.

Localization supports lane-relative planning and interaction, but accurate pose alone does not establish legal compliance or collision avoidance. Perception, prediction, planning, control and the physical environment still matter. Define how excessive uncertainty or detected inconsistency affects the supported capability and evaluate the complete response.

A useful interview follow-up is to distinguish global map position from relative position to a nearby obstacle, and explain why improving one does not automatically improve the other.