Detailed Notes on Coordinate Systems and Mapping Techniques

Geographic Coordinate Systems (GCS)
- Definition: A GCS uses angular units to describe a location on an ellipsoid or a model of the Earth.
- Key components: Latitude and longitude
- Latitude ranges: -90 to +90
- Longitude ranges: -180 to +180
- Usage: Tells the program where to draw data.
Projected Coordinate Systems (PCS)
- Adds a layer of projection to the GCS, reducing distortions when mapping.
- Function: Provides a flat visual representation of the earth's surface.
- Note: No projection can completely eliminate all distortions; some are better than others.
- Example: Web Mercator preserves direction but distorts area.
- Distortion types: Area, shape, and size can become distorted when using only a GCS.

Why just GCS leads to data distortion
- When bringing GCS data into a two-dimensional space, such as a computer screen, it stretches and distorts values, especially at higher latitudes.
- Example: Demonstrated using the Washington dataset in Lab 3.
Adding a PCS
- Essential to specify how the layer should be drawn.
- Without a PCS, the program assigns a default, often causing further distortion.
- Importance of choosing a proper projection according to the spatial analysis needs:
- Distance preservation
- Area preservation
- Direction preservation

Each mapping area may require different GCS and PCS:
- U.S. maps commonly use NAD83 or WGS84.
- Other regions (e.g., Europe, Australia, Asia) use their specific models based on geographic needs.
Components of a Coordinate Reference System (CRS)
- A CRS can be purely geographic (GCS) or be enhanced by a projected system (PCS).
- Key identifiers such as EPSG codes help distinguish these systems (e.g., EPSG: 4269 for NAD83, EPSG: 2911 for NAD83 UTM zone 11).

How to identify the CRS in files
- Open layer properties to review descriptive information.
- Indicators:
- A forward slash followed by the PCS designation signifies a projected system.
- Units in degrees indicate a GCS; units in feet/meters indicate a PCS.
Data Input and Projection Change
- To change the projection:
- You cannot simply rename or set the CRS through the software; a copy must be created.
- Use the "export" or "save as" feature and select a new CRS.
- The program will apply mathematical algorithms to convert the original CRS to the new one.

The PLSS is not a projection but a method for mapping and claiming land.
Understanding PLSS terminology:
- For example, "Southwest quarter of the South half of Section 11, Township 4 North…" indicates parts of land subdivisions.
Primarily used in rural areas, less applicable to urban planning.

Types of Maps
- Each map type serves various audiences and purposes (e.g., physical, political, thematic).
- Importance of design in conveying information clearly.
Map Definition (according to National Geographic)
- A map is a flat representation of selected characteristics that communicates information about the world.
Iterative Map Design Process
- Feedback and adjustments improve overall clarity and usability of a map.
Print Layout and Aesthetics
- A map must provide a balance between aesthetics and functionality; it should be visually appealing yet informative.

Coordinate Reference Systems (CRS): Understanding their roles in mapping accuracy.
Projections: Differences between GCS and PCS, and the data representation they provide.
Importance of Proper Selection: The right projection must be chosen for accurate mapping in different geographical areas.
Understanding PLSS: Significance and limitations of the Public Land Survey System.
Cartographic practices: Types of maps and the map-making iterative process for effective communication and representation of spatial information.