The patterns at the top and bottom
consist of 46 blocks (at each edge) of 5 rows of 7 bits. Taking dark=0 and light=1, these are readily intrepretable as ASCII characters.
If my hand-decoding (it seemed like marginally less effort than writing a program to pull them out of the image) is correct then here's what they say:
34224/54091/ /50545/30396/ /34112/00696/ /NNNNN/ /11111/00501/68646/ /00310/10885/ /12211/61950/ /WWWWW/#####
34334/97766/ /32142/26439/ /53334/04347/ /NNNNN/ /11111/22101/10376/ /31251/36185/ /05444/37088/ /WWWWW/#####
34444/94173/ /10145/03590/ /22340/08060/ /NNNNN/ /01111/92101/63036/ /30532/35788/ /03215/84256/ /WWWWW/#####
3344U/3302U/ U/0054U/7220U/ U/0635U/9040U/ U/NNNNU/ U/1101U/0171U/7031U/ U/1550U/3550U/ U/4504U/0390U/ U/WWWWU/####U
where I should explain that
I have divided each edge into two sets of 23 blocks; each group of 5 characters is one block; slashes are just to indicate block divisions; spaces are literal space characters;
# means not a literal hash character but a carriage return (character 13); and
U is a literal U but I think it's actually serving as padding or corruption -- it's the pattern 1010101 that you can see a lot of along the bottom.
The observant reader will immediately notice that
each block of 23 has the form 00 00 00 N#000 00 00 W where 0 indicates digits and N,W indicate actual N or W characters repeated. I will be flabbergasted if these are not map coordinates.
The most obvious thing to do (though it actually isn't the first that occurred to me) is
to treat each "single-pixel" row as containing two locations (except that the last has only one) and see where they are. It doesn't look as if the path joining them forms writing or anything like that, so let's just take a look at the places.
35°53'30"N 106°01'16"W [P] Cities of Gold casino, Pojoaque Pueblo, Santa Clara, CA
44°00'40"N 108°00'21"W [M/W] middle of nowhere, Worland, WY
20°53'16"N 156°38'29"W [L] "The L" school, Lahaina, HI
29°49'19"N 104°18'15"W [S] middle of nowhere, Shafter, TX
41°56'26"N 116°05'10"W [O] The Crater, Owyhee, Duck Valley Reservation, NV
39°32'50"N 121°33'03"W [R] middle of nowhere, Oroville, Sacramento, CA
47°26'34"N 120°16'57"W [E] nowhere in particular, Wenatchee, WA
37°14'33"N 113°21'40"W [L] nowhere in particular, Leeds, UT
36°43'34"N 107°58'48"W [B] nowhere in particular, Bloomfield, NM
46°29'47"N 116°15'48"W [O] middle of nowhere, Orofino, Nez Perce Reservation, ID
39°10'20"N 096°33'08"W [KS] nowhere in particular, Manhattan, KS
44°03'28"N 123°05'34"W [O] Skinner Butte Park, Eugene, OR
41°15'30"N 110°57'22"W [E] Evanston Water Treatment Plant, Evanston, WY
47°49'46"N 103°38'15"W [A] middle of nowhere, Alexander, ND
43°50'00"N 116°28'56"W [E] middle of nowhere, Emmett, ID
33°07'09"N 107°13'40"W [T] middle of nowhere, Truth or Consequences, NM
33°02'60"N 110°55'53"W [R] middle of nowhere, Kearny, AZ
40°52'34"N 073°55'09"W [C] The Big C Rock, New York, NY
42°40'50"N 111°00'40"W [F] middle of nowhere, Fairview, WY
These are all
land locations in the United States
and one thing that jumps out at me is that
all of them have big letters, visible in the Google Maps satellite images, near them. (At first I thought some didn't, but closer inspection finds such letters near them all.) I've put them in square brackets. For the one saying KS, the actual location given is more or less on top of the K so it may just indicate the letter K. In the order I've put them in above it doesn't seem as if they spell anything, nor do they if I arrange them in the same configuration as on the borders of the card. They do form (without too much moving around, either) an anagram of POWELLS BOOKSTORE CAFE; perhaps that is our place.
Powell's have four shops in Portland, OR; one in nearby Beaverton, OR; and none anywhere else that I know of. I'm not sure any but the main one ("Powell's World of Books") is big enough to have a cafe. So let's suppose we're aiming for that one. (I wondered briefly whether the picture on the card was of a church in Portland or Beaverton near to the right bookstore, but that doesn't seem to pan out.)
We could still do with some confirmation of where we are going, and with figuring out when. Well, one possibility is to look at
the text of the postcard -- e.g., first and last letters of the sentences or something. I haven't so far found anything hidden there, though.
Another conspicuous thing is
that wording "eight score and seven", which is surely a deliberate reference to the Gettysburg Address. The date on which that was given, November 19, doesn't seem to be a national holiday in the US (though it is e.g. International Men's Day); in some states Lincoln's birthday (February 12) is a holiday, and in the US as a whole Lincoln is commemorated together with Washington on Presidents' Day (third Monday in February; in 2018 this will be the 19th). But these all lead to dates that are either in the past or too far in the future to be plausible (surely Sam wants to meet up quite soon).
So, let's consider
what holidays there are that lie a little more than 167 days in the future. It seems like we want ones celebrated in the US. Well, St Patrick's Day (which I'm not sure is a holiday anywhere, but is quite widely celebrated) is on 2018-03-17 which would give us Sunday 2017-10-01 -- perhaps the picture on the card is of a St Patrick's church or cathedral? It looks like one bit of St Patrick's Cathedral in Dublin -- see e.g. at the left of this image, enough so for me to be pretty sure this is the intended meaning, but it doesn't seem to me like the glass in the window quite matches: in every recent picture I can find of St Patrick's, that window has horizontally-oriented rectangular panes. But perhaps they are a recent addition and the picture on the card is an old one? Perhaps the picture on the card is of the transept opposite to the one whose end is visible in that photo? In any case, one can see a window with the right sort of structure at about 0m22s in this YouTube video of St Patrick's.
So, so far, I reckon
Carl should probably meet Sam in the cafe at Powell's City of Books in Portland, OR. He might try Sunday 2017-10-01 which is 167 days before St Patrick's Day, but the reasoning behind this is a bit sketchy. I haven't seen anything to indicate what time of day.
Things I'm not happy about yet:
I haven't got very strong evidence of which Powell's. There might be other anagrams of those letters, too. I am not certain that the picture is really of St Patrick's Cathedral. There's nothing indicating when in the day Carl should meet Sam. (Perhaps that's a good thing. If Sam's going to be there all day, Carl will have time to check all the Powell's stores.)