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The reason you're seeing this behaviour is that you're doing two asynchronous calls (to d3.json) that are not independent of each other because of the way you're selecting elements and binding data to them. By the nature of asynchronous calls, you can't tell which one will finish first, and depending on which one does, you see either the correct or incorrect behaviour.

In both handler functions, you're appending path elements. In the first one (for the world file), you're also selecting path elements to bind data to them. If the other call finished first, there will be path elements on the page. These will be matched to the data that you pass to .data(), and hence the .enter() selection won't contain all the elements you're expecting. This is not a problem if the calls finish the other way because you're selecting quake elements in the other handler.

There are several ways to fix this. You could either assign identifying classes to all your paths (which you're doing already) and change the selectors accordingly -- in the first handler, do .selectAll("path.country") and in the second .selectAll("path.quake").

Alternatively, you could nest the two calls to d3.json such that the second one is only made once the first one is finished. I would do both of those to be sure when elements are drawn, but for performance reasons you may still want to make the two calls at the same time.


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