Question

This is for a GIS class working with ArcGIS and ArcMap. I don't know how to approach this.

You can define the coordinate system in three main ways. That is using the Select, Import and New options. Briefly describe how each are different.

Answer 1

Data usually comprises an array of numbers. Spatial data is similar, but it also carries numerical information that allows you to position it somewhere on earth. These numbers are part of a coordinate system that gives you a frame of reference for your data, to locate features on the surface of the earth, to align your data relative to other data, to perform spatially accurate analysis, and to make maps.

All spatial data is created in some coordinate system, whether it is points, lines, polygons, rasters, or annotation. The coordinates themselves can be specified in many different ways, such as decimal degrees, feet, meters, or kilometers—in fact, any form of measurement can be used as a coordinate system. Identifying this measurement system is the first step to choosing a coordinate system that displays your data in its correct position in ArcGIS Pro, in relation to your other data.

Coordinate systems

Data is defined in both horizontal and vertical coordinate systems. Horizontal coordinate systems locate data across the surface of the earth, and vertical coordinate systems locate the relative height or depth of data.

Horizontal coordinate systems can be of three types: geographic, projected, and local. You can find out what coordinate system your data is in by examining the layer's properties. Geographic coordinate systems (GCS) most commonly have units in decimal degrees measuring degrees of longitude (x-coordinates) and degrees of latitude (y-coordinates). The location of data is expressed as positive or negative numbers: positive x- and y-values for north of the equator and east of the prime meridian, and negative values for south of the equator and west of the prime meridian.

Spatial data can also be expressed using projected coordinate systems (PCS). Coordinates are expressed using linear measurements rather than angular degrees. Finally, some data may be expressed in a local coordinate system with a false origin (0, 0 or other values) in an arbitrary location that can be anywhere on earth. Local coordinate systems are often used for large-scale (small area) mapping. The false origin may be aligned to a known real-world coordinate or not, but for the purposes of data capture, bearings and distances may be measured using the local coordinate system rather than global coordinates. Local coordinate systems are usually expressed in feet or meters.

Vertical coordinate systems are either gravity-based or ellipsoidal. Gravity-based vertical coordinate systems reference a mean sea level calculation. Ellipsoidal coordinate systems reference a mathematically derived spheroidal or ellipsoidal volumetric surface.