Conversion　of　points　or　lines　from　vector　to　grid　format,　or　vice　versa,　is　the　first　operation　required　for　most　spatial　analysis.　Conversion,　however,　usually　causes　the　location　of　points　or　lines　to　change,　which　influences　the　reliability　of　the　results　of　spatial　analysis　or　even　results　in　analysis　errors.　The　purpose　of　this　paper　is　to　evaluate　the　change　of　the　location　of　points　and　lines　during　conversion　using　the　concepts　of　probability　and　entropy.　This　paper　shows　that　when　a　vector　point　is　converted　to　a　grid　point,　the　vector　point　may　be　outside　or　inside　the　grid　point.　This　paper　deduces　a　formula　for　computing　the　probability　that　the　vector　point　is　inside　the　grid　point.　It　was　found　that　the　probability　increased　with　the　side　length　of　the　grid　and　with　the　variances　of　the　coordinates　of　the　vector　point.　In　addition,　the　location　entropy　of　points　and　lines　are　defined　in　this　paper.　Formulae　for　computing　the　change　of　the　location　entropy　during　conversion　are　deduced.　The　probability　mentioned　above　and　the　change　of　location　entropy　may　be　used　to　evaluate　the　location　reliability　of　points　and　lines　in　Geographic　Information　Systems　and　may　be　used　to　choose　an　appropriate　range　of　the　side　length　of　grids　before　conversion.　The　results　of　this　study　may　help　scientists　and　users　to　avoid　mistakes　caused　by　the　change　of　location　during　conversion　as　well　as　in　spatial　decision　and　analysis.　(C)　2018　International　Society　for　Photogrammetry　and　Remote　Sensing,　Inc.　(ISPRS).　Published　by　Elsevier　B.V.　All　rights　reserved.