country-borders | Latitude/Longitude dataset for country borders

The enter selection does what you are trying to do without the use of .each(). Bostock designed D3 to join data to elements so that:

Instead of telling D3 how to do something, tell D3 what you want. You want the circle elements to correspond to data. You want one circle per datum. Instead of instructing D3 to create circles, then, tell D3 that the selection "circle" should correspond to data. This concept is called the data join (Thinking with Joins).

I suggest that you take a look at some examples on the enter, update, and exit selections. Though, it is possible that you were originally doing this with the plain circles (and identical tooltips):

The US json that you reference is a special json file - it doesn't need to use a projection. Your path variable uses a null projection (the default projection), converting the coordinate in the geojson (to which the topojson is converted) to pixel values without a transformation.

This file might have been created to allow simpler blocks showing d3 functionality by skipping projection details, but in any event it is relatively unique because of how it is projected.

Each vertex in that US json file has been converted from a latitude/longitude pair representing a point on a 3 dimensional earth to a cartesian x,y coordinate representing a plane with a width of 960 and a height of 500 (the width and height of a bl.ock's default view). Your world data still contains latitude longitude pairs and therefore needs to make use of a projection.

A give away that your data is unprojected is that it is upside down, which results when converting latitude longitude data to pixel coordinates in svg without the transform that defines a projection. The north pole is at 90 degrees north, the equator at 0 degrees. When working with SVG, a y coordinate of zero will be at the top of the screen, a y coordinate of 90 will be 90 pixels down. Thus, the north pole will be below the equator when converting latitude longitude points to x,y svg points with no conversion. Further, the western and southern hemispheres have negative x and/or y values, so they won't appear in your svg without a transform. This is why you see only points east of the prime meridian and north of the equator on your map.

How to fix this? You need to project your data. You could use any one projection, I will use a mercator as it is probably more recognizable than others (despite major distortion issues near the poles):

The reason why text is not coming up is because: you have not specified any location where it need to come up.

For circles you are giving a cx and cy but nothing for the text.

A better approach would be to make a group like this: