WHAT
Need to see the location of natural or man-made features and phenomena and how they geographically relate to each other.
WHY
2D maps are the most familiar type of presentation for road maps since they resemble paper maps. 2D maps allow analysts to superimpose spatial data which is visible at a certain scale because the eye of the user looks at it from above.
WHEN
Use 2D (planar, overhead, flat) maps when location of or the relationships between elements of some space, such as objects, regions, or themes is important. Furthermore an overhead perspective on a flat surface allows easy comparison of color-coded points and polygons without being obstructed by three-dimensional buildings.
HOW
Every point on a 2D map is viewed from directly overhead, the viewpoint is at infinity so the viewer looks vertically down the z-axis along parallel projection lines[1]. This means that there is no obvious indication of elevation since the map is only represented using the x and y coordinates.
Since 2D maps are lacking the ability to visualize the third dimension, consider using cartographic techniques like contour lines, spot heights, hill shading, or hypsometric color to substitute the missing z axis.
EXAMPLES
References
[1] https://geographx.co.nz/services-products/3d-maps/