ing
<ul>
<li>defined by the gravitational potential of the earth</li>
</ul></li>
<li>a <strong>datum</strong>: earth’s surface that is aligned to the geoid
<ul>
<li>defined by the alignment of the ellipsoid to the geoid</li>
</ul></li>
</ul>
</section>
<section id="projected-coordinate-systems-pcs" class="slide level2">
<h2>Projected Coordinate Systems (PCS)</h2>
<ul>
<li><p>The surface of the earth is curved but maps (and to data GIS) is flat.</p></li>
<li><p>Projected coordinate systems have an origin, 