A map is composed of many layers of information, each displaying different geographic features. This is literal as well as figurative because at the very beginning of a map's creation, its spatial data is divided up into many separate files.
The files are imported into mapping software where they are displayed in a layered fashion, one on top of the other. Layer order is important. To ensure the features display correctly, are not obliterated or overprinted, careful organization is necessary.
There are two data types maps are made with: vector and raster.
VECTOR: editable points, lines and areas all containing attributes (further information about every feature - this could be which direction a river flows, how wide it is, how deep it is etc.) Vector data is shown as a geometry described by vertices.
To make editing and symbolization more straightforward, features with similar characteristics are grouped together.
Generally, map layers follow a feature type pattern to their structure: area features are often placed near the bottom with line features above and point features on top. The topmost layers are annotation - text - labelling the features shown on the map.
Within each general data group, there may be dozens of individual layers also displayed in a particular order to maintain proper readability. For instance, there may be three or four different types of transportation networks - roads, railroads, trails, bicycle paths. There may be several types of point features: populated places, capital cities, mountain points, etc. All these individual layers, too are placed in a logical order so all reads accurately and well.
Though maps are widely varied in their types and subject matter, each have geographic material in common. The similarities consist of the features providing the backdrop for the rest of the map's information - this is called a basemap. Basemaps show the fundamental qualities of the terrain including countries, states/provinces or municipalities (depending on scope and scale); lakes, rivers, and coastlines. The level of detail is determined by the scale of the map.
RASTER: is image based data containing information within a matrix of pixels.
Each pixel has a value representing a specific piece of information such as elevation in that exact spot. Raster data is often used for specific analysis and can be very useful in showing things like landcover, temperature changes, and flood risk.
Examples of raster data include hillshades, satellite imagery and aerial photographs, though pictures and scanned materials may also feature in a map.
Many basemaps are built on a backdrop of shaded relief.
Hypsometric tint adds dimension and context to shaded relief.
Maps, especially smaller scale ones, often have a graticule.
When each layer of of data has been symbolized, edited and put in a precise order, the map comes alive:
Every map is composed of numerous layers and pieces of data all coming together to display its story and information.
