Document rules for file naming and directory structure

MAINTENANCE.md

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+# Maintainers Guide
+
+This page contains information about the GMT data server.
+
+## Naming of the remote files
+
+The remote files have names following the pattern:
+
+	planet_name_rru_reg.suffix
+
+in which:
+
+- *planet* can be *earth*, *moon*, *mars* et al.
+- *name* is the name of the dataset, like *relief*, *mask*
+- *rru* is the grid resolution. *u* is the unit, and can be **d** (degree), **m** (minute) or **s** (second)
+- *reg* is the grid registration. It can be either **p** (pixel) or **g** (gridline)
+- *suffix* is the grid suffix. It can be *grd* or *tif*.
+
+## Grid registrations
+
+GMT serves up both pixel and gridline registered files if possible.
+
+If users don't specify a registration, the default registration will be returned.
+
+- GMT<=6.0 returns the gridline-registered version for backward compatibility.
+- GMT>=6.1 returns the pixel-registered version unless only the gridline-registered
+  file is available.
+
+## Organization of directories
+
+The layout of the directories and files on the data server look like:
+
+```
+cache: [Odds and ends used for tests and examples tutorial etc.]
+geography: [The coastline data]
+	dcw
+	gshhg
+server: [Data served by us]
+	earth
+		earth_age
+		earth_day
+		earth_night
+		earth_mask
+	    earth_relief
+		...
+	moon
+		...
+	mars
+		...
+```