Assuming the Interviewer is from Google.
Interviewer (I): How will you map the ocean?
Me (M): What do you mean by mapping? Do you want to map the floor of the oceans?
I: Yes, among other things.
M: Other things could be mapped include : flora, fauna, volcanic vents, sunk objects, minerals etc.?
M: What are the goals for Google to map the ocean?
I: Just as we have mapped land, we want to map the oceans too.
M: Do you have any time frame for this to be complete?
I: We would like to give ourselves 10 years.
M: I know you have said oceans, but do you want to map ALL water bodies (seas, bays, lakes, ponds etc both natural and man-made).
I: Yes, but we would like to first start with the oceans, seas and bays.
M: Are there any other constraints that I should know about, for example cost?
I: No, at this stage we would like to explore all potential ways. Cost decisions come later.
M: I’m no expert in this area, but these are some of the ways I would attempt to use:
First, I would look at the technologies that have been previously used to see whether I can reuse any of them.
Ships: Sonar equipped ships – Advantage lesser cost. Better granularity. More time consuming. Probably effective only in shallower parts of the ocean and seas. Affected adversely by surface weather.
Submarines: Use sonars and lasers etc to map the base of the ocean. Use other sensors to probe for material composition. High cost of acquisition, potentially governmental regulations involved, high cost of operation, and high granularity of detail.
Drones/Planes: Low flying drones: Less expensive. Potentially can cover large areas quickly. Multiple drones can, in parallel, scan large areas of the ocean. Probably less effective in deep parts of ocean. Lower granularity of detail.
Satellites: Potentially least effective. Very high cost.
Based on the above analysis and the time deadlines. I would use a combination of drones/low flying airplanes fitted with appropriate sensors, in conjunction with submarines for finer detail where needed to map the oceans.
I would test the technologies in lakes of various depths to make sure I can fine tune the technology before taking it to deeper oceans.
I would also hire “oceanologists” who will serve as subject matter experts to guide this project from a technical standpoint.