– Even if you are OK with remembering numbers, much of the world is poorly addressed So let’s reference every 3x3m space on the Earth with a unique combination of three words What Three Words grid
9/15/2015 9 What Three Words grid speared.subs.luckiest What Three Words – questions… Is this truly a geospatial system ? – (Does it have any topology ?) What about languages? How dependent on smartphone/device access?
9/17/2015 1 Polar Stereographic projection Two main zones – north and south: 2.5 UPS Coordinate System North: UPS Coordinate System South:
9/17/2015 2 UPS Coordinate System - gridded Gridded for Military Grid Reference System (MGRS) - Same as UTM
9/22/2015 1 2.3 Map scale & spatial resolution When acquiring or creating spatial data – it imperative that you assess the quality & appropriateness of the data – specifically in regard to your project needs Some issues involved here: – map scale – spatial resolution – accuracy – precision – data lineage See also pp. 199-202 in the textbook Map scale Map scale : the ratio between map distances and Earth distances. Something from the Earth… (a geographic entity or phenomenon) …is scaled to be mapped at a much smaller size (a geographic data object) Can be expressed in different ways: • Rep. fraction (RF) : “1:50,000” • Verbal scale : “1 inch = 2500 feet” • Graphic scale : 0 50 100 mi
9/22/2015 2 Remember that map scale is a ratio Expressed as: “1 to _______” or “1:_______” = 1 / _______ (representative fraction, or “RF”) Question: What is large scale ? small scale ? Larger scale or smaller scale…? Two scales of commonly available US topo maps: – 1:100,000 vs. 1:24,000 ? US road atlas: – map of the Northeast US vs. map of NYC each filling a page of a book? Map of Africa: – classroom wall map vs. textbook map ?
9/22/2015 3 General classification of scale: Large scale – 1:250 to 1:25,000 – example: Data produced by towns, cities Intermediate scale – 1:25,000 to 1:250,000 – example: National mapping data Small scale – 1:250,000 to ?? – example: Mapped information in an atlas (a necessarily arbitrary breakdown) Map scale You must always be aware of the implications of map scale when using geographic data Map scale is linked to the related issues of precision/resolution and accuracy
9/22/2015 4 Map scale & spatial resolution A crucial implication: An analog map’s spatial resolution : smallest physical mark that can accurately be drawn on an analog map = smallest geographic feature or distance that can accurately be represented on that map » this is directly related to the scale of the analog map Map scale & spatial resolution A crucial implication (continued): Why? Consider the relationship between the size of that smallest mark that can be drawn on the map and smallest object in the real world than can be represented on the map …
9/22/2015 5 Map scale and spatial resolution Spatial resolution on an analog map = the best possible spatial precision that can be derived from that map (NOTE: not necessarily the map’s accuracy!)
- Fall '08
- Map projection, Universal Transverse Mercator coordinate system, Coordinate systems, GIS data models