Carte choroplèthe - Données de réponse des pompiers

Question

<\/HEAD>Bonjour,<\/P> <\/P> Je suis dans la 4e semaine de "Going Places with spatial analysis" et j'ai une question de suivi concernant les données de réponse des pompiers. Comme nous l'avons appris en classe, pour créer une carte choroplèthe, il est préférable de normaliser les données pour une comparaison précise entre les zones. Ils mentionnent qu'avec les données sur la criminalité, vous compteriez le nombre d'appels puis diviseriez par la superficie. Je ne suis pas sûr de ce que cela signifie.<\/P> <\/P> Avez-vous des suggestions sur la manière de normaliser correctement mes données de réponse incendie afin de les utiliser dans une carte choroplèthe ?<\/P> <\/P> Merci, <\/P> Brent<\/P><\/BODY><\/HTML>

BrentVan_Scoy__Fire_ · Answer

Yes is a fantastic response. I recall reading the intensive data verus extensive data in an article this week.

Understanding Statistical Data for Mapping Purposes

I will have to go back and compare what you are describing as it pertains to fire departement response data.

Thank you for the comments.

Brent

hhet · Answer

dividing a total "count" by an areal extent will give you a relative measure of your variable.

the final units are aka density.Density is a relationship.

in arcGIS 10.1 , you use Layer Properties to draw quantities using symbol size to show relative value by chooosing the appropriate fields for both Value and Normaliztion.

Larger areas may or may not influence the numerical values you want to classify. What you are doing in this calcaulation is deriving  spatially intensive data from spatially extensive data. dividing one sum (as in, summary statistic) by another sum will yield you a spatially independent (of size) unit. Note that areas and perimenters are also considered summary statistics.

if you split the areal unit and recalulate (but first you make the basic assumption that the counts are uniformly distributed across the area),  the density value will remain the same as before but the counts and the area will not say the same. Proportions, though calulated differently than density, are also spatially extensive.

spatially extensive data should not be used to symbolize a chorolpleth map although this mistake is made over and over again by the uninitiated

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BrentVan_Scoy__Fire_ · Answer

Hi Robin,

I will give that a try. I just normalized it by square miles, but I like the idea of the population also.

Thank you for the reply.

Brent

Omaha Fire Department