I use a shapefile with CRS ("+proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0"). I want to calculate a buffer around the points with 'extract' from raster package. How can I know the units in this layer? Is it in meters? My idea is to calculate 1X1 km , thus buffer=1000. Is that correct?
try1 <- extract(raster, points, fun=mean, na.rm=T, sp = TRUE, # create spatial object buffer = 1000, method='simple', weights=T, normalizeWeights=F) +proj=longlat is in angular units, degrees by default.
Better if you can project your dataset before, to a conformal projection (to preserve the circular buffer shape) appropriate for your work area (so that the distance deforms as little as possible).
ogr2ogr for the points and gdalwarp for the raster. United States is a large area, and it's not easy to preserve shapes and distances in larges areas. Is your work area the whole country or can it be a smaller area? I'm used to projecting in transverse mercator, tangential to an internal point of the work area, but I usually work with smaller surfaces.