Choropleth mapa - Data o zásazích hasičského sboru

Question

<\/HEAD>Dobrý den,<\/P> <\/P> Jsem ve 4. týdnu kurzu "Going Places with spatial analysis" a mám doplňující otázky týkající se dat o zásazích hasičského sboru. Jak jsme se učili na hodině, pro vytvoření choropleth mapy je nejlepší data normalizovat pro přesné porovnání mezi oblastmi. Uvádějí, že u dat o kriminalitě byste spočítali počet volání a pak vydělili plochou oblasti. Nejsem si jistý, co to znamená.<\/P> <\/P> Máte nějaký návrh, jak správně normalizovat moje data o zásazích hasičů, aby bylo možné je použít v choropleth mapě?<\/P> <\/P> Děkuji,<\/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