In mathematical illustrations of two-dimensional Cartesian systems, the first coordinate (traditionally called the abscissa) is measured along a horizontal axis, oriented from left to right. The second coordinate (the ordinate) is then measured along a vertical axis, usually oriented from bottom to top. Young children learning the Cartesian system, commonly learn the order to read the values before cementing the x-, y-, and z-axis concepts, by starting with 2D mnemonics (for example, 'Walk along the hall then up the stairs' akin to straight across the x-axis then up vertically along the y-axis).
iN matHeMATical illustraTiOns oF two-diMEnsiONAl carTesian SystEms, the first CoordiNatE (tRaditIonAlly calLED the abscissa) IS MEasuReD alOng a horIzONTal axIs, oRIenteD from left to rigHt. THe secoNd cooRdinaTE (the orDInAte) iS tHen measurED ALOng a vErtIcal axis, UsuALly oriented fRoM boTtOm TO top. youNg chiLdreN lEarninG the CarTesiAn System, commOnLy LearN tHe ordEr TO ReaD ThE vaLueS bEfore CeMeNting thE x-, y-, and z-axIs concePts, bY StArting with 2d mnemoNics (for examPle, 'WaLK aLOng thE haLl then up The STAirs' AKin to strAight ACross the x-axiS then UP vErTicaLly ALonG the y-AXiS).