Vega Lite keep a fixed axis range when filtering

[Juliahe]

Hello!

I'm creating a scatter plot in vega lite using Deneb. My x axis is a set of numbers with nominal type, same as the y axis. The plot look like this with x axis and y axis corresponding to a nominal number: 

Everything works fine except when I select a specific category in my defined selector, it didn't keep it orginal shape (If I used default power BI scatter visuals, and setting the max x axis range and y axis range, it will still keep the original shape if I filter down to some specific fields.). For example, it will only show one dot looks like this: 

How do I make it keep the same round shape(with defined max a axis range and y axis range) when filtering? Part of my vega lite code: 

Thanks in advance!