Okay, piece of advice - remotely detailed distance measurements is the last thing you need in your story. Instead of trying to measure and write down distances and sizes, vast majority of cases it's better if you focus on impressions, shapes, and comparisons instead. Metaphors and exaggerations can also be useful, but those shouldn't be overused.
The simplest example would replacing "he stood about a hundred meters away - she recognized him by the red cap on his head" with be something like "he stood much farther next to the towering buildings - enough she had trouble recognizing his face, but his red cap caught her eyes". There's no actual distance there, but why is it good?
One, it compares that bit of description with another, allowing to smoothly visualize the scene. You could say one thing is five meters tall and another is seven, but that still requires the reader to parse that information and process it. When you read one thing is taller almost by a half though, you can immediately tell how they compare to each other. And in the example, the person is compared to the huge buildings close to him, immediately conveying how small his figure is without any detailed descriptions.
Two, it appeals to the reader's imagination. You can always say someone stood a hundred meters away, but that's just a fact. How does he look? What's noticeable? By itself, it's not a great way to convey distances, but it can be used to greatly enhance the mental image of the scene - rather than describing an objective state, you describe a subjective view, which massively helps with immersion.
You can use those in various different situations, such as "the gnarled tree creeped out of the dense fog so close it almost seemed to wrap around the pair" or "my eyes snapped there and I squinted, trying to get a better look at the vague shape moving in the distance".
