Surfaces and features

In 3D Analyst, you model reality with surfaces and features.

Surfaces model a phenomenon that varies continuously across an area. Elevation, precipitation, and soil pH are all phenomena suitable for modeling with surfaces.

Elevation, precipitation, and soil Ph are types of phenomena that vary continuously across a landscape. With an infinite number of possible values, these types of data are best represented with surfaces.

Features represent entities with discrete boundaries. Buildings, wells, telephone poles, and roads are all examples of data modeled as features. In each case, there is a clear boundary or distinction between the features.

This map shows parcel, hydrant, and street features. There are a limited number of possible features of each type, all of which have clear and definable boundaries.

Distinguishing feature from surface data

A clear distinction occurs between feature and surface data if you consider the following:

· Feature data is countable. For example, you can count the number of parcels, streets, or hydrants within a city.

· Values modeled with surfaces are not countable. If you think they are, try collecting an elevation value for every square meter in your local park. Once you finish the job, recollect the elevation values for every square centimeter. If you are truly a masochist and complete this task too, reduce the sampling distribution to every square millimeter and collect the values again. As you can see, this madness could go on indefinitely leading to an infinite number of elevation values, or at least until the you reached the precision of your measuring instrument.

In 3D Analyst, surfaces are represented by rasters or TINs. Features are represented by 2D or 3D feature classes, such as shapefiles and geodatabases.