Cartography, GIS, and Data Management
What this domain tests
Data stewardship: choosing a projection, documenting accuracy and lineage, converting between CAD and GIS, and refusing to let a map imply precision the data does not have.
Projections and coordinates
Conformal projections preserve angles and local shape at the cost of area; equal-area projections do the reverse. Distance distortion grows away from standard parallels and the central meridian. Every layer in a project should share a defined coordinate system and datum; reprojecting is not the same as transforming between datums.
Vector, raster, and topology
Vector features carry attributes and support topology rules (no gaps, no overlaps, connectivity). Raster data stores a value per cell, so its accuracy is bounded by cell size. Parcel fabrics need tie points to the PLSS and a record of monument vs. computed corners.
Documentation and accuracy
Metadata should record source, date, datum, accuracy, and processing steps. Federal-style horizontal accuracy is reported as 1.7308 × RMSEr at 95% confidence. "Tax parcel" layers are for assessment; they are not survey documents and should carry a disclaimer.
Generalization
Cartographic generalization (elimination, simplification, displacement) means the minimum mapping unit controls what appears. At 0.5 mm of map resolution, features narrower than that are dropped rather than drawn.
Worked example
A 1:24,000 map is compiled at 0.5 mm minimum line width. Ground equivalent = 0.5 mm × 24,000 = 12,000 mm = 12 m. An irrigation ditch 3 m wide cannot be represented faithfully at that scale, so its depiction as a single line tells the user nothing about width. Similarly, digitizing that map at 1:1,200 does not make it a 1:1,200 dataset.
Traps that cost marks
- Treating a reprojected layer as if a datum transformation had occurred.
- Computing areas in a projection and reporting them as ground areas without a scale-factor correction.
- Delivering parcel GIS data without an accuracy statement or disclaimer.
- Confusing resampling (a new cell size) with improved source accuracy.