Question 19 of 23: Organizing Map Data into Layers

Question 19: Organizing Map Data into Layers (5 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Map data is organized into thematic layers (historically called coverages) — each holding one type of feature such as roads, hydrography, parcels, contours or land use — because this modular structure is what makes a GIS flexible and analytically powerful. Separating themes lets the user display only the layers relevant to a task and combine them selectively, so a single database can serve many different maps and analyses. It allows each theme to be captured, edited and updated independently, with its own accuracy, currency and custodian, without disturbing the others; a road layer can be revised while the parcel layer stays untouched. It permits each theme to use the most appropriate data model and attribute schema (vector parcels, raster elevation) and to carry its own symbology. Above all, layers are the basis of overlay analysis: because features are registered to a common coordinate framework, layers can be stacked and intersected (e.g., overlay soils, slope and zoning to find suitable sites), which is impossible if everything is merged into one undifferentiated map. Layering therefore supports selective display, independent maintenance, thematic reuse, model flexibility and, most importantly, spatial overlay and multi-criteria analysis.