A sentence you can quote
Aspect ratio describes the rectangle. Resolution describes how finely that rectangle is sampled. 3840×2160 is still 16:9; it is not “more widescreen” than 1280×720.
Why the two searches stay apart
One search wants the distinction between shape and pixel count. Another wants a single size’s ratio, megapixels and uses, and that belongs on the size page. This guide does not reuse those titles.
Megapixels sit with resolution
MP = W×H/1e6. A 1:1 1080×1080 frame is 1.1664 MP, far below 1920×1080 at 2.0736 MP, even though the square can look larger on a phone. A poster can be 4:3 at 300 DPI while a television is 16:9 at 1920×1080. Scaling both sides keeps the shape and only changes how many samples fill it.
When both change
Cropping 16:9 to 9:16 changes ratio and usually resolution. Scaling 1920×1080 to 1280×720 keeps the ratio and drops resolution.
A side-by-side you can quote
1920×1080 is 16:9 and 2.0736 MP. 1280×720 is also 16:9 and 0.9216 MP. 1920×1200 is 16:10 and 2.304 MP. Same width, different ratio, different megapixel count. That trio is the whole distinction: shape can stay put while the pixel count changes, and the pixel count can stay in the same ballpark while the shape changes.
Search aspect ratio vs resolution when you want the distinction. Search a pixel pair, such as 1920×1080, when you want that size’s ratio and megapixels. The titles are written so the two intents do not collide.
Frequently asked questions
Is 1080p an aspect ratio?
No. It is a height. 1080×1920 is also 1080p-class in portrait.
Can two resolutions share a ratio?
Yes. That is the entire 16:9 family.
Can two ratios share a width?
Yes. 1920×1080 vs 1920×1200.
Which should I set first?
Pick the ratio the platform asked for, then a resolution it accepts.
Where is the 1920x1080 page?
At /1920x1080-aspect-ratio/.