So, Tammy VanDeGrift, our Local Arrangements Chair, provided some guidance that I'll share here -- this is not to replace such things as awareness, traveling in groups, and commonsense.
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Here are the "safe" places near downtown and the convention center:
Downtown: Close to the hotel is safe
The waterfront is safe (park along the river for walking/jogging)
Shopping district is safe (near Pioneer Place)
Pearl District is safe (lots of condos, cafes, restaurants, the "newest" yuppie part of downtown)
Convention Center: Close to convention center is safe
Near Lloyd Center (shopping mall) is safe during mall hours (closes at 9 PM)
Along Broadway and Weidler Streets is safe during shopping hours (until 9 PM)
Less safe areas (at night):
MLK Blvd, Williams, Vancouver Streets (north of convention center)
East side of river (near OMSI)
Chinatown (downtown), lots of homeless shelters nearby - may not be unsafe, but pan-handling could be distracting
Under the Burnside Bridge (homeless camps at night)
Gresham (along MAX stops, but this town is a suburb and I doubt anyone would venture out here)
Portland is generally a safe place, with very few incidents. I have never felt uncomfortable walking around at night downtown, but I would suggest that people walk with at least one other person
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For the record, Susan and I have visited Portland without incident -- we walked across the Burnside Bridge one evening and did pass a number of homeless, so we will just take the MAX or walk another bridge in the future.