The map with overlayed position information shows an arc of possible last positions given the position of the satellite that received the last known signal.

Edit: the satellite getting ACARS pings is apparently geosynchronous, so triangulation is not possible, but...

What is the arc of the final position based on? The Earth is not flat, and geosynchronous satellites are at about 36,000 km altitude (compare to Earth's radius of about 6375 km). Shouldn't the position, if based on ranging from a geosynchronous satellite, be much closer to a straight line (and actually dipping to lower altitudes in the center)? Why does the graphic appear to depict a range from a point low over the Indian ocean rather than a point in geostationary orbit?

What possible location or ranging information could create an arc like that? If the ping was not to a geosynchronous satellite, that raises questions—the ping couldn't have been from the ACARS system, and it would mean triangulation might be possible.

Could it be a range from a low earth orbit satellite, or an over the horizon communications system? In the middle of the Indian ocean? The only thing even close to that is Diego Garcia, but the illustrated location is several hundred miles north of Diego Garcia. I'm discounting over-the-horizon radar, because I think that would have to mean they knew which blip was the missing plane, and isn't the only way to know that to be tracking it?

What about the second to last known signal, or the third to last? Given that we're not talking about arcs from points low over the Indian ocean, but from a point in high orbit, and the plane can only be within an ~8 mile slice from max altitude to the ground, and given that the earth is also curving away from the satellite, how can the arc of possible positions from the final ping cover that much ground?

Australia has radar coverage of some of the southern area where the plane might have been. Are we to believe nobody's checked Australian radar logs to eliminate part of the southern arc of final positions depicted?

Is this search being run by incompetent officials, or are they releasing purposefully incomplete or inaccurate information to the press, or is there some mysterious reason why they generated an arc like that from a geosynchronous satellite and why prior ACARS pings or radar logs don't help narrow the search area at all?