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Scale problem in ArcMap 9.3

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#1
Jeanette

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I'm fairly familiar with most of the features in ArcMap, but every once in a while I have a minor issue that I just don't know how to fix. I am doing a thesis that will measure accessibility, and I am having a serious scale issue. All shapefiles are projected in NAD 1983 StatePlane Ohio North FIPS 3401. The problem is that the scale bar and any distance measurements are way off: what should be a mile is being measured as about 0.000001 miles, and a 1/4 mile buffer around a location comes up as encircling the entire map. Also, the representation box is saying that "1 inch = 0 miles." Please tell me there is a simple fix that I am missing? Thanks!

#2
frax

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Check the units settings for the data frame and in the options dialog. It may be that the scale you see is not in miles, but in degrees?
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#3
jrat

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Double check your projection you might be in meters.

#4
Jeanette

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In the data frame properties, the map units are in meters, but I had changed display to miles, which didn't help. But even the meter measurements are off; a distance that I know to be a mile measures at 0.018 meters. Is it a projection problem? Two of the shapefiles are from the US Census (streets and county block groups), the third is a file made by geocoding addresses. I've used these data sources before and not had this problem.

#5
DaveB

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Most likely the projection assigned to some (or all?) of the data is incorrect. From your description of the scale that's being displayed and the measurement differences it sounds like your data is actually in a geographic coordinate system rather than a projected coordinate system. One quick way to "sanity" check this is to look at the Layer Properties dialog in ArcMap, go to the Source tab and check the Extent section. If you see values under 360 it's likely the data is in degrees. If the data is in meters or feet it's more likely you would see extents in the 10s or 100s of thousands or more. So it might be all you need to do is redfine the coordinate system of the incorrect layers to a geographic coordinate system, most likely NAD 83 from the Geographic Coordinate Systems. Caution: Make sure you don't reproject it; just redefine it.

This ESRI knowledge base article might help. It talks about finding the correct projection for data that has no projection defined, but you can remove the projection info from your data and then follow the article. I would try working with one layer at a time in a new ArcMap session.
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#6
kass

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It might not be a projection problem. I ran into this issue recently with another user. In that particular case, they were using two data frames (one for a small-scale vicinity map). When you create the scale bar, the bar is tied to the active (not selected, although normally they're the same) data frame, and in this case, the wrong data frame was active when the scale bar was inserted. I couldn't find a way to determine which data frame the scale bar is referencing after its created, so ended up deleting it and inserting a new one with the correct data frame active. It was tricky to troubleshoot - hopefully this helps.




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