Not really sure what you mean with "the real place". Also would be nice to know which engine. For Unreal 4 I would recommend checking out the documentation here, there is almost everything you need to know for importing a heightmap: https://docs.unrealengine.com/latest/INT/Engine/Landscape/TechnicalGuide/
That seems to be some sort of DEM heightmap. These maps are really large in scale. The area you have imported is probably hundreds of kilometers across so you can't really have that in engine unless you cut it down to a reasonable size. But if you have downloaded that from public domain before you ask how to rescale that to fit real life scale, you should ask how much of an area this heightmap is covering at all? How would you know what the width and length of that piece of heightmap is in real life is something you can find out if you are using MicroDEM or these sort of programs to prepare the heightmap. Otherwise there's no way to figure it out unless you spend hours lining it up on google maps and then use the ruler to see what the dimensions are.
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Also would be nice to know which engine.
For Unreal 4 I would recommend checking out the documentation here, there is almost everything you need to know for importing a heightmap:
https://docs.unrealengine.com/latest/INT/Engine/Landscape/TechnicalGuide/
https://docs.unrealengine.com/latest/INT/Engine/Landscape/TechnicalGuide/index.html#recommendedlandscapesizes
Then when you import your heightmap in UE4 it'll create a landscape of that size in Kilometers.
But if you want to go beyond 8km x 8km you need to use world composition.
https://wiki.unrealengine.com/World_Machine_to_UE4_using_World_Composition
https://docs.unrealengine.com/latest/INT/Engine/Landscape/Custom/index.html
https://docs.unrealengine.com/latest/INT/Resources/ContentExamples/Landscapes/index.html