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63          <h1 class="glimsTitle">GLIMS: Global Land Ice Measurements from Space</h1>
64          <h1 class="subtitle">Monitoring the World's Changing Glaciers</h1>
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93        <p>
94The GLIMS Glacier Database was originally designed to contain rich data on not
95only glacier outlines, but the physiographic context of different parts of each
96outline.  Outlines were to be composed of segments that when joined together
97would form a complete outline, and these segments could have associated
98attributes unique to them, such as what materials (rock, vegetation, snow, ice,
99…) were on the left and right sides.  Similarly, nunataks (rock outcrops
100internal to a glacier) were represented with separate polygons so that they
101could carry attributes separately from the glacier outline.  </p>
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103        <p>
104As the GLIMS community and database grew, actual patterns of data production
105and use diverged from this initial design.  Researchers provided glacier
106outlines not as collections of segments, but as complete outlines, with “holes”
107(inner rings) representing nunataks.  The Randolph Glacier Inventory (RGI) used
108this same simpler data model.  These differences were accommodated by
109on-the-fly data transformations during both data ingest (holes-to-polygons for
110nunataks) and data download (nunatak polygons-to-holes).
111        </p>
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113        <p>
114To align the data model with actual use patterns, we completed a project to
115simplify the database schema and associated software (input and output).  </p>
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117        <p>
118The database contents are almost completely the same in the new data model.
119Representation of image metadata, people and their affiliations, literature
120references, and so on, remain unchanged. The following changes resulted from the
121new simpler data model:
122        </p>
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124<ol>
125<li>Nunataks (rock outcrops internal to a glacier) are represented by holes in
126the glacier boundary polygon rather than separate polygons.  The old download
127interface offered a choice between these two representations, but most people
128downloaded data in the “holes” format.  A query sent to the GLIMS mailing list
129in late 2024 about the possible loss of the "separate polygon" option elicited
130no complaints.</li>
131
132<li>The vast majority of the small topological errors in some glacier outlines
133have been fixed.  These tend to be small self-intersections that can be fixed
134with minimal modification to the outline.</li>
135
136<li>Multi-polygons, as well as multiple outlines that share a glacier ID, have
137been converted to single outlines, each with its own identity.  Thus, the
138glacier IDs have changed for some entities.</li>
139
140<li>Many tables have been eliminated, such as those that stored individual
141segments of an outline.</li>
142
143<li>A few fields have been removed, such as the "local" and "global"
144uncertainty fields.  This is because those values were fairly arbitrary in
145practice, and one can know these uncertainties from knowledge of the imagery
146used.</li>
147
148<li>The download interface has become more streamlined, since the data model
149(number 1 above) is now "holes" only.  Also, the experimental "RGI-on-demand"
150feature has been removed for now.</li>
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