I'm looking for a free enc so I downloaded this one https://charts.noaa.gov/ENCs/Agreement.shtml?US2EC02M. After unpacking I have a file US2EC02M.000 and CATALOG.031 What should I do with those? I wanted to display it in a .Net app I'm creating using SharpMap. I thought it's packed and tried to unzip using 7z but I'm getting an error.

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The .000 file is in S57 format. This is a standard, but rarely seen in my experience, geographic data format. That is mentioned here: https://charts.noaa.gov/ENCs/ENCs.shtml

If you need to convert it to another format for your application then you can use the ogr utilities or load into a GIS such as Open Source QGIS and save in the format you need.

Note it has a lot of layers in it so you might also want to learn how to filter out the layers you want, and what they all mean.

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I don't know what the CATALOG.031 file format is but it just seems to be a big descriptive text block of what's in the folder:

002623LE1 0900073   660400000000190000000001000048000019CATD0001220000670000;&   0001CATD0100;&   ISO/IEC 8211 Record Identi
fier(I(5))1600;&   Catalogue Directory FieldRCNM!RCID!FILE!LFIL!VOLM!IMPL!SLAT!WLON!NLAT!ELON!CRCS!COMT(A(2),I(10),3A,A(3),4
R,2A)00101 D     00053   550400010000600000CATD000420000600000CD0000000001CATALOG.031V01X01ASC00119 D     00053   5504000100
00600000CATD000600000600001CD0000000002US2EC02M\US2EC02A.TXTV01X01TXT2B0AE6C200119 D     00053   550400010000600000CATD00060
0000600002CD0000000003US2EC02M\US2EC02B.TXTV01X01TXTEBFC546A00119 D     00053   550400010000600000CATD000600000600003CD00000
00004US2EC02M\US2EC02C.TXTV01X01TXT256F3F3400119 D     00053   550400010000600000CATD000600000600004CD0000000005US2EC02M\US2
EC02D.TXTV01X01TXTA1B8205600119 D     00053   550400010000600000CATD000600000600005CD0000000006US2EC02M\US2EC02E.TXTV01X01TX
T853438CE00192 D     00053   550400010000600000CATD001330000600006CD0000000007US2EC02M\US2EC02M.000Cape Hatteras to Straits 
of FloridaV01X01BIN26.366669-81.66666735.333333-67.1636517988833C

I don't know what "Sharpmap" is or what files it can read. But now you know they are S57 files you can consult the documentation and see if Sharpmap can read them.

Note also they are vector files (ie points and lines and polygons), not raster files (like an image).

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