Derkalz,
Hello and welcome to the Guild! As I have no experience with computer program assisted mapping as of yet (haven’t yet had the time >.<), I can only speak on readability, functionality, and self-consistency. I am sure many others are much more qualified to advise on textures and the like.
For a random encounter, I find your work to be quite impressive! I often will scribble a generic stretch of road, segment of forest, etcetera, and a table of possible baddies with a table of possible things the baddies are doing. Focusing on the map and not the balance of the encounter, I think you have a really good idea started! The shape of the area provides room for different combat tactics, which is one of the best things to build into a combat map. After all, isn’t the idea of an open world game to be able to do as you please? The tree in the center really pops, and draws the eye in, and the circular pathway offers a refreshing contrast to the ridged artificial shapes of the tomb stones and pillars.
In the fledgling stage of your map, I see a few structural points that raise question, the first being the bushes that frame your battlegrounds. To the left and right you have openings where the bushes do not enclose around the entombed king, and unless there is something I am missing a character standing where the path meets the roundabout would be able to see far beyond where your map ends. This might cause problems mid combat when players try to go off map, or utilize the undefined to their advantage. It also gives a rather unfinished feel to the map due to a lack of boundaries. Perhaps have it close off to help define the map? Moving on, it seems to me that the entire orientation of the tombs, pillars, and even the tree are a bit off. Drawing a straight line down the center of the incoming path has it cut through the 10th tomb (counting clockwise from the entry path), and the spacing between each tomb is different. The tree doesn’t seem centered within the inner meadow, and each of the pillars (were the pillars ever holding something up? Where are the remains of the rest of that structure?) are spaced and oriented differently around the edge. Unless the insanity of the “Mad King” is being personified in these ways, I would recommend rebuilding with the Tree as your center, and everything else measured from there. Speaking of the tree for a moment; if this is a battle map, what is the diameter of the tree? How much space does it take up that the players on the ground are unable to simultaneously occupy? Can it be used to hide behind? Can two hide behind it? Three? The branches are nice for identifying where a player can climb to and offer a bit more immersion, but aren’t very useful for combat beyond that. Trees make top-down views a bit tricky, as the base is smaller than the crown, and a footprint is hard to discern with a grid overlay. Speaking of a grid, will you be using a hex or square grid, or perhaps your players enjoy measuring out range with tape? If the latter of the three is true, how do you find that works for you? What are the shortcomings?
I would like to divert from your map a moment to discuss the theme of your map, as necromancy is tied with aberrations as my favored topic within fantasy (especially in D&D). Presuming the necromancer is innocently going about his/her business, attempting to simply get by and raise an undead family to better the world (as most are want to do), I would think he/she would have created an alter to better perform the necromantic rituals. Such mounds are often built upon desecrated/unholy land, which causes plant life to wither and twist. Unless the entirety of the grounds are desecrated (which would lend to the possibility of the dead getting up for a midnight stroll on their own without the aid of a necromantic civil servant) this holy, unholy, mundane variations in the land would create distinct patterns in the overall shape and color of the land. Remember, dead things grow when necromancy magic is applied, so why not apply that to the plants to the area? This will give the necromancer time to animate the dead who then have to claw their way up 6 or so feet of hardened earth. Though I will not question why there is a king not entombed in a warded/protected family crypt, I will recommend the royal guard be properly armed and armored to help support their being buried nearby. If you would like some more ideas on necromancy I will happily discuss it!
In conclusion, I enjoy the theme and concept of your map! A few things would need to be adjusted before I would be able to use it effectively for combat, but the potential for greatness is there! I look forward to seeing your work develop. Thank you for sharing your work!