University:
California State University, Northridge
Course:
GEOG 340 | Economic Geography
Academic year:

2024
Views:

406

Pages:

2
Author:

esgrilhi90j

Measures Spatial Central Tendency You have no doubt calculated the average for a set of numbers in grade school or junior high. You may recall calculating means, modes and medians. Geographers are also interested in calculating these figures, but geographers do so with spatial data and so the formulas look slightly different. Perhaps the most basic measure of central tendency is the Mean Center. It's calculated much the same way as a numerical average, but instead you would use coordinate points. Xc= Sum of Xi/n and Yc= Sum of Yi/n where: Xc = Mean of all X coordinate points (Xi's - like latitudes) Yc= Mean of all Y coordiates points (Yi's - like longitudes) n = number of observations (or points) One could use this formula to find the average position among a group of points. Be warned though, the result produced by this formula can be highly affected by outliers, or points that are far away from the rest. Frequently, geographers add "weights" to this formula, because all points may not be equal. There may be different populations or frequency of events at these points and such additional data is important. This is called a Weighted Mean Center. The formula would be transformed and would appear as: Xwc= (Sum of Xi*w)/(Sum of w's) and Ywc= (Sum of Yi*w)/(Sum of w's) where: Xwc = Weighted Mean of all X coordinate points (Xi's - like latitudes) Ywc= Weighted Mean of all Y coordiates points (Yi's - like longitudes) W = weights (like population, customers, or freqency of events at the point) The figure below is from the ESRI software you'll be using for this lab.