Beginner here. Im trying to model the earth below. I'm a bit unsure about the approach I should take to do the engraved lines across a solid sphere similar to the image below? For the continents I was thinking of applying a height map of the continents (white continents, black oceans), but I'm thinking I would need to resolve the engraved lines on the object first as it might cause issues with the ocean map? Thanks for the feedback in advance
I would do all the hard work with shaders, using only a UV sphere (smooth shaded). Take an equirectangular black and white image of the world (I used one from here - http://planetpixelemporium.com/earth8081.html) - The 10K version looks best.
Use UV texture coordinates for the image. Because you want the continents "up", you need to invert the image so the continents are white instead of black going into the bump node. The "grid" is just made from Wave textures (one on the X axis and one on the Y, and mixed together). You can see I clamped the "waves" rather thinly using the colorramps and mixed the result with dark grey - this both "softens" the strength of the wave "grooves" as well as giving the whole image a darker look (as this part will go in the oceans which need to stay dark relative to the continents so the continents still "pop out").
From here, it's just a matter of mixing the two together (the grid and the map image), using the original image color as a mask. You can see I softened the result again (with white this time) because this looks more natural. You could do the same thing by altering the strength of the Bump node, but, I use the white mix (or black, depending on need) as a matter of habit as I find it gives me more control over the strengths of individual elements that will eventually be part of a bump map, because sometimes they need to be mixed together (as in this case with the dark).
Lastly is just a matter of increasing the Metallic and lowering the Roughness:
BONUS - you can make the world "glow" like your image by mixing your result with an Emission Shader using a Fresnel as a Mix Factor:
If there isn't a reason you need the sphere to be all one object, I'd be very tempted to make the sphere with engraved lines, and then the country landmass overlay as a separate object (likely parented to the sphere to allow for transformations to still line up.)
This has some advantages. You can have a different geometry resolution for each separate object, which is good as you'll need pretty complex geometry for the landmasses no matter how you choose to model them, and probably don't want or need that much resolution across the sphere, just enough to make the engraved lines look good.
Two approaches to actually constructed the gridded sphere are as follows: You could bevel out a UV sphere and either extrude the large faces or inset the edges. Issues with that would be very visible at the poles, though that might not be a concern.
You could instead duplicate a UV sphere, and on one of them remove the faces and convert the edges into a wireframe (via the wireframe modifier) which you then boolean difference to cut into the original sphere. This is for sure easier, but I suspect the topology will be less controllable. On the plus side, this is a dynamic option that you can resize and adjust later if need be, wheras the other method would be quite hard to adjust after the fact. I'd probably go with this for that reason. It produces something that looks a bit like this, though you could certainly adjust it to be smoother, with more operations performed on the wireframe or base mesh before the difference modifier.
Actually creating the continent mesh from a heightmap (or other source image) seems like a task for geometry nodes. Something like this produces a workable starting point, though I'm just using a specular map of earth here so lakes are cutting holes and you probably don't want that, but that's just a choice-of-image issue.