Key Concepts for Maps

Understanding some key concepts related to shapefiles will help you use the Map Conversion Utility effectively.

A shapefile provides the geographic information for drawing a map. There are three types of shapefiles that the Map Conversion Utility supports:

  • Point. The shapefile identifies the locations of points, such as cities.
  • Polyline. The shapefile identifies paths and their locations, such as rivers.
  • Polygon. The shapefile identifies bounded regions and their locations, such as countries.

Most commonly, you will use a polygon shapefile. Choropleth maps are created from polygon shapefiles. Choropleth maps use color to represent a value within individual polygons (regions). Point and polyline shapefiles are typically overlaid on a polygon shapefile. An example is a point shapefile of U.S. cities overlaid on a polygon shapefile of U.S. states.

A shapefile is comprised of features. Features are the individual geographical entities. For example, features may be countries, states, cities, and so on. The shapefile also contains data about the features. These data are stored in attributes. Attributes are similar to fields or variables in a data file. There is at least one attribute that is the map key for the feature. The map key may be a label, such as country or state name. The map key is what you will link to a variable/field in a data file to create a map visualization.

Note that you will be able to retain only the key attribute or attributes in the SMZ file. The Map Conversion Utility does not support saving additional attributes. This means that you will need to create multiple SMZ files if you want to aggregate at different levels. For example, if you want to aggregate U.S. states and regions, you will need separate SMZ files: one that has a key identifying states and one that has a key identifying regions.