If you're using Davies Locker to get the coordinates, note the following.
As the coordinates are missing the minutes of latitude and longitude. each step is roughly 4-5 minutes.
(trivia- if you graph Sosaria in 3D it turns out to be doughnut-shaped fragment/shard, indeed).
If using only the Classic Client, get a sextant.
If using the CC with UOAssist, use the command -where
If using the EC, there's settings that allow you to see your exact location's coordinates.
First step.
Find the point closest to the zero point that the Davies Locker gives, and drop something to indicate it. This will be one corner of a square for a search.
- If the coordinates are N Latitude, E Longitude, this marker will be the Bottom Left corner of the square.
- If the coordinates are N Latitude, W Longitude, this marker will be the Bottom Right corner of the square.
- If the coordinates are S Latitude, E Longitude, this marker will be the Top Left corner of the square.
- If the coordinates are S Latitude, W Longitude, this marker will be the Top Right corner of the square.
Second step.
Find the other 3 corners of the 1 degree by 1 degree square, and mark them as well. This will create a square that is at worst a 16x16 box.
Third step.
Depending on your amount of Mining skill, you will have to be more accurate in your searching. So, start at one corner, and walk 1-3 steps (depending on your mining skill, the less Mining, the fewer steps), then attempt to dig the map in all 4 directions (in case you missed and were actually standing on it to start). If you don't find it, make another incremental move, and try all 4 directions again.
When you hit the far wall of the square, move slightly across the square (depending on which corner you started with, and which direction), and go back tracing the next row across, making digging attempts.
This is called "Mowing the Lawn". It's used by real world treasure hunters on land with metal detectors, and at sea using sonar and magnetic anomaly detectors. You, though, have a lot better of an idea where to start looking than they do. Provided you didn't misread N/S or E/W or the facet, you will find the chest within 10 minutes under most circumstances - maybe 15-20 if you are doing this with 0 mining, and having to dig EVERY ONE of the 225 or so spots in the square.
The big worry, really, is going by the map, not the coordinates. Some people's clients (like mine) are demonstrably BADLY ORIENTED (see the pic below of one of my digs). I've had maps show the entire pin on one side of a river, then the chest is on the other. Use the map to get to the area, but the actual coordinates to attempt to dig.
