This picture shows where Isidis Planitia is on Mars. The Mars globe on the left shows how Mars would look to your eyes if you were close to Mars. The globe on the right shows how high (or low) places on Mars are. Places that are high look red or orange on the right globe. Places that are low look green or blue on the right globe. You can see that Isidis Planitia is low because it is blue.
NASA/JPL/Malin Space Science Systems and the Mars Orbiter Laser Altimeter (MOLA) Team at NASA's Goddard Space Flight Center